Ninety-two cases of granulosa cell tumor of the ovary have been studied. The clinical and pathologic data from this group were similar to that obtained in previous series. Because of the long natural history of many granulosa cell tumors, crude death rates over a relatively short period give little indication of the true malignant potential of these neoplasms and hence corrected survival rates were calculated; these show that, if no patient died from any other disease, approximately half of the women with this neoplasm would die, as a result of the tumor, within 20 years. Factors indicating a relatively poor survival rate were: age over 40 at the time of diagnosis, a presentation with abdominal symptoms, a palpable mass, a solid large tumor, bilateral tumors, extraovarian spread, and numerous mitotic figures in the tumor. It is suggested that all granulosa cell tumors should be considered as malignant and that the factors pointing to a poor prognosis are those indicating that a particular tumor has been diagnosed at a late stage in its natural history, either because it has been present for a long time or because it is highly malignant. There are no definite criteria for defining the prognosis in a case in which the tumor has been removed at any early stage in its natural life history.