Thirty-nine patients underwent primary surgery for epithelial ovarian tumors of low malignant potential at the Massachusetts General Hospital between 1970 and 1980. Eighty-five percent of patients were found to have Stage I disease and 15% were found to have Stage III disease. Fifty-four percent of patients had a tumor with serous histology, 39% had a tumor with mucinous histology, and the remainder of patients had tumors with an endometrioid or mixed-cell type. Second malignancies and benign ovarian tumors were frequently found concomitantly with the borderline tumors or in follow-up. Gastrointestinal and endometrial adenocarcinomas were the most common second malignancies and were frequently found associated with a borderline tumor of serous histology. Follow-up was available in all 39 patients (100%). Mean time of follow-up was 11.8 years. Sixty-nine percent of patients are clinically without evidence of disease with a mean follow-up of 14.7 years, 23% died of other causes, 5% died of disease, and 3% died with disease and sepsis. All patients dying with disease did so within 7.3 years of their primary surgery. Seven patients underwent conservative surgery, defined as preservation of some ovarian tissue. Six of 7 patients are clinically free of disease with a mean follow-up of 14.6 years; 1 patient died of other causes. No patients treated conservatively had a recurrence of their disease.