PIP: There has been speculation as to what constitutes sufficient investigative clinical data to establish the efficacy of oral contraceptives. The obstetric and gynecology advisory board of the U.S. Food and Drug Administration has recommended that 4000-5000 woman-cycles of treatment yield a meaningful pregnancy rate before the oral contraceptive is termed effective. A clinical experience with oral contraceptives is presented. 4977 patients were treated through 51,544 woman-cycles with only 1 questionably unplanned pregnancy. If this pregnancy is considered as a method failure, it represents a pregnancy rate of .02. In such a study, when no pregnancies occur, the upper confidence level for pregnancy probability may be statistically calculated. From the data available it appears that the U.S. Food and Drug Administration's obstetric and gynecology advisory committee recommendation of 4000-5000 cycles will provide the physician with a statistically significant evaluation of efficacy.