Prognostic factors were studied in 770 cases of carcinoma of the ovary treated at Radiumhemmet during 1974 to 1979. Centralization of the treatment in a well-defined population with complete follow-up permits a nonselective study of the disease. The analysis was made separately for early and late stages. For the early cases, histology and grading were the most dominant prognostic factors. For the most advanced cases successful surgical treatment, either primary or secondary, showed significant relation to survival. Successful secondary surgery could be achieved in twice as many cases where radiotherapy was included in the treatment. Even for the advanced cases, the stage but not the histology was of prognostic significance. The major difficulties in evaluating treatment of ovarian cancer, especially in advanced cases, are associated with the multiplicity of sites of the disease and the prognostic factors that may contribute independently to the outcome.