A controlled trial of an oral contraceptive in the treatment of 18 boys with haemophilia is reported. During the treatment with combined oestrogens and progesterone we found a reduction in bleedings of the skin and joints, associated with a minor shortening of coagulation time in glass and plastic as well as a decrease in kaolin‐cephalin time. Correspondingly, there was a significant increase in fibrinogen and factor II + VII levels. The treatment did not affect the number of days in bed, haematuria, epistaxis or muscular bleeding. ‐ Because of this rather negligible effect and since all patients developed severe side effects (gynaecomastia and pubic hair), we do not recommend this treatment in the general management of haemophilia.