The biologic behavior of serous tumors of low malignant potential (LMP) is of significant interest, yet most large series lack extended follow-up. This study consists of 200 patients: 106 patients were diagnosed with serous tumors of LMP at our institution between 1979 and 1984 and an additional 94 patients were identified in the referred tumor registry. The patients ranged in age from 6 to 98 years (median, 34 years). The stage distribution was Stage I in 135 patients (67.5%), Stage II in 24 patients (12%), and Stage III in 41 patients (20.5%). Follow-up information from 4 to 27 years (median, 10 years; mean, 11.2 years) revealed 155 patients (77.5%) were alive without further evidence of disease and 11 patients (5.5%) died of unrelated conditions without recurrent tumor. Thirty-four patients (17%) developed recurrent neoplasms at 6 to 145 months (median, 26 months). Patients with Stage III disease developed recurrent neoplasms more commonly (54%) than did patients with Stage I or II disease (6 and 17%, respectively). Following treatment of recurrence, 15 patients are free of disease, 6 patients are alive with disease, and 13 (6.5% overall) patients have died of disease 1 to 15 years (median, 5 years) after their initial diagnosis. Mortality was also stage dependent: 0.7, 4.2, and 26.8% of patients with Stages I, II, and III disease, respectively, died secondary to tumors of LMP. Clinical life table analysis demonstrated 5-, 10-, and 15-, and 20-year survival rates for all stages of 97, 95, 92, and 89%, respectively. These findings confirm the excellent prognosis for patients with serous tumors of LMP, even when long-term follow-up is extended to 20 years. Additionally, these data suggest that those with more advanced or recurrent disease can enjoy extended survival.