The clinical aspects and pathologic findings in 44 cases of pure clear cell carcinoma of the ovary are presented. The patients ranged in age from 28 to 78 years (mean, 50.6 years); 54% were nulliparous. Thirty-three percent of the patients had endometriosis in the involved ovary, and an additional 25% had endometriosis only in sites distant from the tumor. Microscopically, three architectural patterns (papillary, tubulocystic, and solid) and four cell types (clear, hobnail, eosinophilic, and flattened) were seen. A predominant tubulocystic architectural pattern was a good prognostic factor (p less than 0.01); however, no significant difference in survival by cell type was found. Grading of the tumors by conventional architectural and cytologic criteria had no predictive value for survival. Stage at presentation was the most important prognostic factor (p less than 0.001), with a 5-year overall survival of 34% and stage I survival of 55%. The poor stage I survival reflects the 15 patients (34%) in the study with stage Iaii lesions. In the 25 patients who developed recurrence, both distant organ involvement (40%) and lymph node involvement (40%) were frequent. Ovarian clear cell carcinoma has unusual pathologic and clinical features, and it represents a distinct histologic type of ovarian carcinoma.