Granulosa and theca cell tumors of the ovary account for 2-3% of ovarian malignancies. This study includes 54 patients with the diagnosis of granulosa cell tumors of the ovary treated between 1953 and 1987. Median age at diagnosis was 57 (27-83) years. The lesions were staged according to FIGO. The number of patients in various stages was IA, 41; IB, 3; IC, 3; IIB, 6; and III, 1. Median tumor size, 11 cm; range, 0.5-30 cm. Post-menopausal bleeding was diagnosed in 48%, MHC in 37%, proliferative endometrium in 32%, and atypia of endometrial cells in 13% of the cases. Fifty patients were treated with primary surgery, 48 patients were treated with adjuvant external radiotherapy, and 3 patients received complementary chemotherapy. The survival rates in stage I were 94 and 88% after 5 and 10 years, respectively, and in stages II-III were 44% after 5 and 10 years. Overall survival was 90% at 5 years. The frequency of observed mitosis influenced the survival rate: with less or equal 4/10 HPF the survival was 100% in 5 years, with 5-9/10 HPF the survival was 80% in 5 years with a median survival time of 9 years, and with more or equal 10/10 HPF the longest survival was 4 years. At the end of the study, 45 patients (83%) are alive with no evidence of disease, 1 patient is alive with disease, 4 patients are dead of recurrent disease, and 4 patients are dead from intercurrent disease. Endometrial carcinoma was detected in 5 patients. The total survival is better than that with epithelial ovarian cancer as the hormonal symptoms make an early diagnosis possible. Stage for stage the survival is equal. There is an increased incidence of endometrial carcinoma and concomitant other malignancies. The mitotic rate is a well-defined parameter and influences the survival significantly and should be considered the most important prognostic factor at treatment planning.