A retrospective study of 40 female-to-male transsexuals was performed to investigate the frequency of endocrine dysfunction prior to hormonal treatment with testosterone. Two patients had laparoscopic evidence of polycystic ovarian disease (PCOD) prior to androgen treatment. Nine additional subjects had clinical evidence of PCOD, including ultrasonographic evidence of multicystic and enlarged ovaries in three patients and/or evidence of hirsutism and oligomenorrhea associated with increased androgen levels and/or an increased plasma luteinizing hormone (LH)/follicle-stimulating hormone (FSH) ratio. Two subjects had evidence of gonadal dysgenesis. Plasma levels of testosterone, prolactin, LH/FSH ratio, and dehydroepiandrosterone sulfate were significantly increased in 30 female transsexuals prior to testosterone treatment when compared to normal adult female controls studied in the early follicular phase of the menstrual cycle. These data indicate that female transsexuals have an increased incidence of endocrine dysfunction (32.5%) which should be investigated prior to hormonal treatment.