Alan Alda is listed as the only M*A*S*H performer to appear in all 256 episodes.
Alda played Captain Benjamin Franklin “Hawkeye” Pierce, the show’s central surgeon and one of its most consistent characters. He remained with the series from its premiere in 1972 through the finale in 1983, giving him an appearance in every episode of the 11-season run.
The figure of 256 includes the feature-length finale, “Goodbye, Farewell and Amen,” which aired on February 28, 1983. Alda was not merely an actor during the later seasons: he also wrote and directed episodes and became increasingly involved in the show’s creative direction.
Other recognizable performers appeared in many episodes but not all of them. Loretta Swit was a long-running regular as Margaret Houlihan, while Jamie Farr and Gary Burghoff played important recurring or regular characters. Burghoff’s Radar left before the series ended, which is why he does not match Alda’s complete-episode record.