The association between ovarian cancer risk and reproductive factors has been well established, and two main theories, incessant ovulation and gonadotropin stimulation, have been proposed to explain the mechanism. Recent studies using animal models of ovarian tumorigenesis, and analysis of ovarian tissues from prophylactic oophorectomies, suggest that depletion of ovarian follicles might underlie the epidemiological findings linking reproductive history and ovarian cancer risk.