A clinicopathologic analysis of 6 patients with ovarian neoplasms resembling sex cord tumors with annular tubules (SCTAT) was performed. The patients' ages ranged from 20 to 43 years. Most had signs and symptoms of estrogenic hormonal imbalance; none had evidence of the Peutz-Jeghers syndrome. The tumors were unilateral in all cases and, except for one lesion of microscopic size, were from 3 to 18 cm in greatest dimension. One tumor was combined with a germinoma. Surgery alone was the primary mode of therapy in all cases. Lymph nodal metastases developed in 2 patients 7.5 and 10.5 years postoperatively. They are the first documented examples of malignant behavior recorded. At the time of last known contact, all patients were alive without demonstrable tumor for intervals from 1.5 to 16.3 years (mean, 7.8 years) after initial treatment. While the annular patterns of growth have often been attributed to Sertoli cell differentiation, histologic and cytologic features of granulosa cell tumor were observed in areas of the primary tumors and in metastatic lesions. True lumen formation was never observed in the so-called tubules. We propose classification of SCTAT as a distinctive annular and membranous variant of granulosa cell tumor in view of the morphologic similarities and comparable clinical behavior of these two neoplasms.