Gilliam suffered a massive brain hemorrhage at his home on September 15, 1978, and, following surgery, lapsed into a coma from which he did not recover. He died in Inglewood, California, nine days before his 50th birthday, one day after the Dodgers clinched their tenth pennant during his tenure in the 1978 National League Championship Series. His uniform number 19 was retired by the Dodgers two days after his death, prior to Game 1 of the 1978 World Series. His number is the only one retired by the Dodgers of a player not in the Hall of Fame. He is interred in the Inglewood Park Cemetery.