A virilizing, ovarian lipoid cell tumor was removed from a 19-year-old woman with amenorrhea. Light- and electron-microscopic studies of tumor morphology were combined with biochemical measurements of testosterone, dihydrotestosterone, estrone, estradiol, and progesterone. Electron microscopy demonstrated cells with the typical ultrastructural features of steroidogenesis. Analysis of extracts from tumor tissue showed high concentrations of progesterone, testosterone, dihydrotestosterone, estrone, and estradiol. These extracts from the ovarian lipoid cell tumor contained the following quantities of steroids: testosterone 450 ng/g tissue; dihydrotestosterone 56 ng/g tissue; estrone 233 pg/g tissue; estradiol 10896 pg/g tissue; and progesterone 512 ng/g tissue. Ovarian vein blood of the ovary with the lipoid cell tumor showed these results: testosterone 3276 ng/dl; dihydrotestosterone 311 ng/dl; estrone 69 pg/ml; estradiol 258 pg/ml; and progesterone 8.1 ng/ml. Because of the ultrastructural and biochemical similarities of this tumor to granulosa lutein cells it is concluded that this ovarian lipoid cell tumor probably originated from ovarian stromal cells.