Forty-four cycles with a spontaneous luteinizing hormone (LH) surge among 377 in vitro fertilization (IVF) patients were studied for outcome with different timing of oocyte retrieval. Mean number of preovulatory oocytes per retrieval and per transfer was significantly less in these cycles than in controls. Mean number of preovulatory oocytes per retrieval and per transfer was significantly higher when the human chorionic gonadotropin (hCG)-retrieval interval was greater than 35 hours, compared with less than 24 hours. In cycles with an hCG-retrieval interval of less than 24 hours, percentage of preovulatory oocytes was higher when serum estradiol (E2) decreased by greater than 15% on the morning after hCG administration compared with a plateau or an increase in serum E2. Timing oocyte retrieval after spontaneous LH surge should consider the hCG-retrieval interval and changes in E2 levels after hCG administration; this may avoid cancellation for many patients.