We report a case of a 23-year-old woman who was afflicted with disseminated skin erythema multiforme-like eruptions that started at the menarche, relapsed at the premenstrual periods, dramatically spread during two pregnancies and cleared after abortion; the skin lesions responded dramatically to thalidomide treatment. A high-affinity binding factor to 17α-hydroxyprogesterone (17-OHP) was found in the serum of this patient. Her lymphocytes did not proliferate in vitro after exposure to exogenous 17-OHP but showed significant chromatin activation. There was a decreased expression of HLA antigens at the surface of the patient’s blood lymphocytes. This is a unique well-documented case of erythema multiforme most possibly due to autoreactivity to 17-OHP; the precise mechanism(s) of this autoreactivity has not been established.