In vitro fertilization (IVF) was performed in normally ovulatory women after the follicular phase of an unstimulated cycle. Twenty patients initiated 36 cycles of unstimulated IVF, with serial ultrasound examinations and hCG 10,000 IU given when the follicular was mature. Thirty aspirations were carried out under intravenous sedation with transvaginal ultrasound guidance. One or more oocytes were obtained in 29 aspirations (97%) for a total of 52 oocytes (average 1.7); 37 fertilized (71%), two were polyspermic, and 35 cleaved (67%). Seventeen aspirations (57%) yielded multiple oocytes. All 25 oocytes obtained from dominant follicles fertilized (100%), and 12 of 27 oocytes from secondary follicles fertilized (44%) (P < .05 versus dominant follicles), with one polyspermic fertilization in each group. Sixteen cycles resulted in a single embryo transferred (36% multiple ET). Five clinical pregnancies (20% per ET, 13% per retrieval), all sigletons. Our results suggest that in selected cases, IVF in unstimulated cycles may be a clinically viable alternative to stimulated cycles, with preliminary success rates in the range of national averages for stimulated cycles.