The article describes the results of observations conducted on 88 patients on OC (oral contraception) with norgestrienone administered daily in a dose of 0.35 mg for a total of 1131 cycles. There were 2 pregnancies, giving a Pearl index of 1.06%. The only reported side effects were slight disorders in the menstrual cycle. In general this form of contraception was very well accepted, and it must be seriously considered for those patients who cannot tolerate combined OCs, i.e., those patients with antecedents of thrombophlebitis, hypertension, of metabolic problems, and of venous pathology. The article includes an ample review of the literature on the subject, especially the mechanism of action of progesterone only contraceptive agents.