One of a pair of male identical twins developed peptic ulcer at age forty-six. The character of both twins resembled that described by Alexander as typical in peptic ulcer. Why did only one of the pair suffer from ulcer? Apparently the well twin had less rigid defenses against his wishes for dependency, and married a woman who could be kind and loving. The sick twin had more rigid defenses and first suffered from symptoms of ulcer while his wife was disturbed almost to the point of psychosis. The twins therefore differed slightly in character, and circumstances tended to intensify oral conflicts in the twin who became sick.