A 24-year-old woman, gravida 1, para 0, experienced recurrent attacks of headaches and bizarre behavior from the sixth week of gestation onward. Three days before confinement, she lapsed into coma and was delivered of a normal child. Plasma glucose, insulin, and C-peptide levels were diagnostic of insulinoma. Subsequently, after she spontaneously regained consciousness, a pancreatic tumor was removed at laparotomy with complete resolution of symptoms. The problems of diagnosing insulinoma during pregnancy are discussed.