At the 4077th Mobile Army Surgical Hospital (M.A.S.H) unit in Korea, two army doctors by the names of Hawkeye Pierce and Trapper John McIntyre receive some exciting news in the mail. Their Korean house boy, Ho-John got accepted into Hawkeye's old college. Hawkeye and Trapper decide to hold a party filled with music, dancing, and alcohol to raise money for Ho-John's plane trip to the U.S. They achieve this by raffling off a weekend pass with a nurse, Lieutenant Dish for R&R in Tokyo.

Trapper and Hawkeye seek to keep a new nurse from being transferred by Hot Lips, and they vie for her affection. Henry Blake, challenged by another commander to a boxing tournament, makes Trapper fight a big, intimidating soldier in exchange for keeping the nurse at the 4077th. Hawkeye and Ugly John employ the use of a glove soaked with ether to insure Trapper's victory, which impresses the nurse. Margaret and Frank's attempts to unfix the match collapses, as they are flattened by the unconscious boxer!

The 4077th is designated as the setting for the making of an army film on Mobile Army Surgical Hospital units. Hawkeye is chosen as the star while Margaret and Frank compose a screenplay. The Eye Of The Hawk objects to the piece of propaganda that filmmaker Lt. Bricker is producing and, having exposed the original film, reshoots a new one his way, starring himself as Groucho Marx-ish Yankee Doodle Doctor, and poking fun at glorifying doctors while concluding with a rather serious speech about the hell of war.

Henry receives a citation for the camp achieving the best efficiency rating, and then General Hammond reassigns him to Tokyo. Frank then changes the camp to be more military, and he confiscates Hawkeye's and Trapper's still. They use forged passes to go to Tokyo to convince Henry to come back and end up pretending Radar is sick.

A rash of thefts breaks out in the camp. Missing pieces include Frank's silver picture frame, Margaret's hair brush, and Trapper's watch. The camp is searched and everything is found in Hawkeye's locker. Everyone thinks he did it. Hawkeye manages to announce to the camp that the items will be dusted for prints to identify the real thief, and catches Ho-Jon. He needed money to bring his family from the North, and to bribe border guards.

Hawkeye moves a wounded North Korean soldier into The Swamp, rather than let him be shipped out before he's stable. During the night he and Trapper play Dracula, and siphon off a pint of Frank's blood. The soldier then contracts hepatitis, so they have to test Frank without him knowing, and have to keep him away from Margaret and the patients.

The nurses go to extremes lengths to find a date for Nurse Eddie - they won't go out with anyone until Eddie gets a date. The men draw straws, and Hawkeye is the big loser, especially after Eddie nearly kills him in a scene resembling teenage "mating" rituals.

Radar gets a Dear John recording from home. Hawkeye and Trapper try to set him up with a date, but fail. Radar is taken by a new nurse at the camp and she is into poetry and music, so they coach him. Margaret wants to stop the relationship, so Hawkeye and Trapper get between her and Frank until she relents. Radar's "Ahhhh, Bach!" and "That's highly significant," quotes win him the girl.

Hawkeye and Trapper operate on a famous Colonel - after discovering that he is particularly ruthless about sacrificing his men, they come up with a scheme to get him sent back to the states with a little unwitting help from Frank, Margaret, and a drunk Henry.

Frank throws his back out whilst spending the evening with Margaret, and ends up in traction. He promptly applies for the Purple Heart, having been 'technically' wounded at a frontline unit. Tommy Gillis, an old friend of Hawkeye's, is writing a book about the war, and pays him a visit. Later, Tommy is brought into the camp, seriously wounded, and Hawkeye can't save him. A 15-year-old kid is in the hospital to have his appendix out. He joined up to be a hero back home, but Hawkeye has him sent home, giving him Frank's purple heart.

The camp tunes into the Army/Navy football game, only to be shelled and have an unexploded bomb land in the middle of the compound. They ring around trying to identify the bomb, and the camp prepares for the worst. Hawkeye and Trapper are left the task of following instructions to disarm the bomb, which turns out to be full of propaganda leaflets from the CIA.

Hawkeye and Frank argue over Frank's surgical ability. Hawkeye performs a difficult operation and the patient does not recover, as he should. Hawkeye begins to doubt his ability and moves out of The Swamp. He decides to open up his patients again, and discovers a nick in the colon that even Frank admits anyone could have missed.

Captain Kaplan is to be shipped home, but becomes paranoid that something will happen to him before he leaves. He takes the wheel of the jeep to drive to Kimpo himself, but crashes and ends up in plaster. Henry's wife is in labor and gives birth while he has Radar calling the hospital every 5 mins.An entertainer, Jackie Flash, visits the camp to entertain the troops.

Brought on by Frank and Margaret's negative reports, General Clayton assigns a psychiatrist, Captain Hildebrand, to examine the 4077th M*A*S*H unit, to see if it should be disbanded. Henry tells them to be on their best behavior, or else they will be split up. But the 4077th soon begins to act in their traditional, insane ways: the shrink experiences Max Klinger, watches the hijinks of Hawkeye and Trapper John, and witnesses the trysts of Frank and Hot Lips. While Hildebrand confronts the unit on its behaviour, choppers bearing wounded begin to arrive and everyone heads for the OR. The onslaught of casualties shows the 4077th's true side.

An inept North Korean pilot, known as "5 O'Clock Charlie", makes his daily attempt to bomb the ammo dump. Frank puts in a request for an anti-aircraft gun, which is granted when Charlie hits General Clayton's jeep. Frank takes charge of the gun, while Hawkeye and Trapper are determined to prevent him using it, by getting rid of the ammo dump. Frank misses Charlie and destroys the dump.

Radar writes the weekly activity report. Hawkeye operates on a wounded prisoner who grabs a scalpel and attacks the doctors. Frank wants Klinger thrown out on a section 8,so Henry calls in a psychiatrist, Major Freedman. Hawkeye is attracted to a new nurse but thinks she is married. Trapper loses a patient who developed complications during the O.R. fracas with the wounded soldier.

Hawkeye and Trapper want the army to admit responsibility for the accidental bombing of a local village. They fill out a report and Major Stoner arrives to investigate, and leaves with all the evidence. When the story is released it claims that the enemy bombed the village, and the army tries to gag the doctors. But, thinking there could be a medal in it for him, Frank has also put a report together, with copies of all the evidence, including shell fragments, so the army comes clean.

Hawkeye has been in non-stop surgery for 3 straight days without sleep, and the wounded keep coming. He decides to find out who started the war, and sends a telegram to Harry S Truman. After listening to some of Frank's rubbish about the North Koreans wanting better plumbing, he tries to send the officers' latrine to the North Koreans with an offer of peace. Trapper finally manages to sedate him. Trapper (about Hawkeye): "I guess he's just unstable. You see, he took this weird oath as a young man, never to just stand by and watch people die."

Hawkeye operates on a 5-year old Korean boy, and Radar can't find his family. Henry plans to send him to the orphanage, and the camp enjoys his company while they can. Trapper decides to adopt him after consulting his wife, and has to rescue him after he wanders into the minefield. Kim's mother turns up at the orphanage looking for him.

Corporal Walker is being sent home, and he wants to marry his Korean girl so she and their baby can return with him. CID sends Lt Willis to investigate, but when he refuses Hawkeye and Trapper frame him. Hawkeye is upset that a nurse he was pursuing does not approve of the marriage between "a gook" and "one of us".

Majors Houlihan and Burns press charges against Colonel Blake to get him arrested and put Frank in charge, and put Hawkeye and trapper under arrest so that they can't help him. Fortunately for Henry, they escape, and with the aid of Meg Cratty come to the rescue.

Once more Hawkeye writes home to his father: the doctors operate on a soldier with a grenade shot into his body; Hawkeye and Trapper colour the skin of a racist patient, who demanded the right colour blood, while he is asleep; Henry gets a movie of his daughters birthday from home; the officers hold the monthly staff meeting.

A lone sniper has the 4077th pinned down - including Radar and Henry in the shower. The poor boy thinks he's firing on McArthur's headquarters, and a chopper finally comes by and wounds him with gunfire from above, ending the siege. Hawkeye walks out to into the bush to tend to the wounded soldier.

The camp succumbs to the Asian flu, except for Hawkeye and Margaret, who have to do everything themselves. As the others start to recover, Hawkeye falls ill but he still manages to operate when wounded arrive. Finally the others are well enough for Hawkeye to stop working and rest. He is thanked for his service with a commemorative roll of toilet paper.

Hawkeye and Trapper recover from an all night party. Henry gets a barbecue, and Hawkeye puts in a request for an incubator. The Quartermaster turns him down. They locate a Major with 3 incubators, but he won't let them have one. A Colonel tries to sell them one, and then they get into trouble with a General at a press conference. Finally, Radar trades the barbecue for an incubator.

The 4077th and friends convene for their weekly “Medical Conference,” A.K.A. Poker while Radar runs over a civilian and Frank is held hostage in the showers by an enlisted man.

Hot Lips gets depressed and requests a transfer, causing turmoil in the camp.

Klinger pretends to be pregnant. Hawkeye and Trapper operate on General Mitchell's son, and the General gives them 3 days in Tokyo Henry keeps getting calls from Tokyo about what Hawkeye and Trapper are doing. When they get back to the 4077 Frank asked the general for an officers club for the camp. They plot to allow the enlisted men access to the club, and when the General opens it the rules are bent to give his son access, which Hawkeye exploits to give access to all.

Henry returns from a week in Tokyo, to announce that he is in love with a 20-year old girl called Nancy Sue Parker. She arrives for the weekend, and Henry shows her off. Nancy comes on to Hawkeye while Henry is in surgery. Henry is reminded of his wife back home when Radar places a call for him, and he realises it's his wife he loves.

A riotous episode in which Hawkeye will do anything to get a new pair of boots: In order to get Zale to get him some, he must get an appointment for Zale with Futterman, the camp dentist, who will only do it if Henry will give him a pass to Tokyo, and Henry will only grant the pass if Houlihan will get off his back, which she will do only if the guys throw a party for Frank's birthday, with a cake, and Radar will only help get the cake if he gets a date with Nurse Murphy, who will only date someone with a hair dryer, and Klinger won't give up the hair dryer unless he gets a section 8 (and Frank won't sign). Inevitably, the deal falls through, much to the Hawkeye's chagrin.

Private Baker, who is always going AWOL, is desperate for plastic surgery on his nose. Hawkeye gets an old friend, and plastic surgeon, to visit the camp, promising him a nurse called "The Barracuda". They put together an elaborate scheme to perform the operation without Frank or Margaret finding out.

A Korean family set up camp in the middle of the compound. A Korean woman with a baby comes looking for the father, and names Radar. Civilian affairs relocates the family and blood tests prove Radar is not the father.

While there are no casualties, Hawkeye & Trapper crate up Frank while he sleeps and receive gorilla suits through the mail. Henry gets a tan and gives another sex orientation lecture. When the wounded start pouring in again, their own side shells the camp, hitting the generator, and Radar tries to get through to someone to stop the shelling.

The MASH 4077 is visted by General Steele. He wishes to move the camp 5 miles down the road. Hawkeye and Henry are charged with mutiny. And Hawkeye is also charged with impersonating a reporter.

Psychiatrist Sidney Freedman composes a letter to Sigmund Freud during a visit to the 4077, while the rest of the camp endures the hijinks of a mystery prankster.

With the arrival of a shipment of records, Radar plays the part of a disc jockey and helps to get everyone through the incredibly long deluge of wounded.