A 20-year-old woman presented with hyperandrogenism presumed to be due to an androgen-secreting granulosa cell tumor. In order to confirm this unusual presentation, short-term tissue culture steroidogenesis of the granulosa cell tumor and contralateral polycystic ovary was performed. Testosterone and androstenedione were produced only by the polycystic ovary, whereas the tumor was producing estradiol and progesterone. The studies of in vitro steroidogenesis prevented an incorrect interpretation of the clinical presentation.