Four luteinized adult granulosa cell tumors of the ovary in women 22-76 (average 53) years of age are described. Two patients presented with postmenopausal bleeding, one with dysfunctional uterine bleeding and one with amenorrhea. The tumors were all stage Ia, ranged from 2 to 11 (average 5.1) cm in greatest dimension, and were typically solid, lobulated, and yellow. On microscopic examination the most striking feature was the abundant eosinophilic cytoplasm of most of the tumor cells, which resembled the granulosa cells of the corpus luteum. The tumor cells typically grew diffusely, but large nodules intersected by scanty fibrous septa were present in all the cases. Additional patterns present focally included cords or ribbons, nests, and thick trabeculae. The tumors had inconspicuous amounts of fibrothecomatous stroma; foci of stromal edema or myxoid change were present in three cases. The tumor cell nuclei were round, of moderate size, and pale, and many of them had nuclear grooves. There was no significant nuclear pleomorphism and the mitotic rate did not exceed 1 per 10 high power fields. Reticulum stains, available in three cases, confirmed the granulosa cell nature of the neoplasms by disclosing scanty intercellular fibrils in most areas. Immunostains, performed in two cases, showed positivity for vimentin in both of them and for cytokeratin, smooth-muscle actin, and S-100 in one. One tumor from a 75-year-old woman was associated with an ectopic decidual reaction in a periovarian adhesion. This patient had focal, severe atypical complex hyperplasia of the endometrium and focal secretory change in the endometrium uninvolved by the hyperplasia.(ABSTRACT TRUNCATED AT 250 WORDS)