The treatment outcome of 778 patients with stage III ovarian cancer treated by surgery and chemotherapy between 1976 and 1990 in 21 institutions was analyzed retrospectively. Survival of patients treated between 1985 and 1990 was significantly superior to that before 1985 (Kaplan-Meier, p < 0.01). Four year survival rates were found to be distributed from 5 to 52% among institutions (p < 0.001, log-rank test). When survival rates were compared according to the relative dose intensity (RDI) of CDDP administered, patients who were given CDDP RDI > or = 0.9 had a favorable prognosis. The twenty-one institutions were divided into two groups: Standard (total abdominal hysterectomy and bilateral salpingo-oophorectomy) vs. standard+debulking (of as much gross tumor as can safely be performed) according to the operative procedure which was performed in each hospital. It was found that the four-year survival rate for patients treated in hospitals where standard surgery was done was 22.9 +/- 12.2%, whereas that in hospitals adopting standard+debulking surgery was 34.4 +/- 10.1% (p = 0.03, t-test). When the hospitals were divided into 4 groups according to combination of the operative procedure and CDDP RDI, the four year survival rates were 17.5 +/- 8.3% for standard+debulking+CDDP RDI < 0.9, 39.0 +/- 1.4% for standard+CDDP RDI > or = 0.9, 28.8 +/- 11.5% for standard+debulking+CDDP RDI < 0.9 and 37.8 +/- 8.0% for standard+debulking+CDDP RDI > or = 0.9.(ABSTRACT TRUNCATED AT 250 WORDS)