In this study, 347 patients with epithelial ovarian cancer without residual tumor after primary laparotomy, were assigned randomly to receive either intraperitoneal instillation of radioactive phosphorus (32P) or six courses of cisplatin (50 mg/m2). Patients randomized to receive 32P with extensive intraperitoneal adhesions were treated with whole-abdomen irradiation instead of 32P (n = 28). The median follow-up was 62 months. Crude and disease-free survival were similar in all groups. Late bowel complications occurred more often in patients treated with 32P compared with the cisplatin group. The estimated 5-year crude survival rate was as high as 95% in patients with borderline or well-differentiated tumors in Stage I. It is suggested that these patients can be treated adequately by operation alone. Patients with moderately or poorly differentiated cancers in Stage I disease had a 5-year crude survival rate of 75%. In these patients, the relapse risk was high enough to warrant postoperative treatment. The efficacy of adjuvant treatment in this subgroup of patients can only be established in a prospective randomized study comparing postoperative adjuvant treatment with a no-treatment arm. Because of the high number of late bowel complications after 32P treatment, it was recommended that cisplatin be used as standard adjuvant treatment for subsequent controlled studies.