Twenty-five normal ovulatory women underwent three-dimensional transvaginal ultrasonography and blood sampling before and after oral glucose tolerance testing to compare ovarian morphology and circulating hormone levels in the early follicular phase as predictors of the number of oocytes retrieved after gonadotropin stimulation for in vitro fertilization. Serum levels of gonadotropins, inhibins, testosterone, dehydroepiandrosterone sulfate, and estradiol as well as summed ovarian volume were unrelated to oocyte number. Antral follicle number and serum androstenedione level, however, positively correlated, whereas postoral glucose tolerance test (post OGTT) insulin release negatively correlated, with total and mature oocyte numbers. Adjusting for age and body mass index by regression analysis, the serum androstenedione level significantly predicted mature, but not total, oocyte number. The relationships of antral follicle number and post-OGTT insulin release to total oocyte number were additive; each was significant after controlling for the other. In contrast, antral follicle number significantly correlated with mature oocyte number after controlling for post-OGTT insulin release, whereas post-OGTT insulin release was unrelated to mature oocyte number after controlling for antral follicle number. Therefore, early follicular phase antral follicle number positively correlates with total and mature oocyte numbers after gonadotropin stimulation for in vitro fertilization and is linked to androgen and insulin actions in predicting ovarian follicle recruitment by gonadotropins.