Eleven patients treated at the University of Texas M. D. Anderson Cancer Center for recurrent disease after resection of a stage I ovarian serous neoplasm of low malignant potential (SNLMP) are reported. At the time of diagnosis, the age of the patients ranged from 26 to 43 years (mean 33). Seven patients had stage IB tumors and 4 had stage IA tumors. All patients were treated with a total abdominal hysterectomy and bilateral salpingo-oophorectomy. The size of the ovarian tumors ranged from 4 to 15 cm in maximum dimension. Stromal microinvasion was seen in 2 cases, and foci of endosalpingiosis were seen in the peritoneum in 8 cases. Nine patients were treated with radiotherapy and 2 with chemotherapy. The time to recurrent disease ranged from 7 to 39 years (mean 16). Eight tumors recurred in the pelvis or abdomen, 2 in the neck with subsequent abdominal involvement, and 1 in the pleura without abdominal or pelvic involvement. In 10 cases, the recurrent tumors were serous carcinoma, and in 1 case it was a SNLMP. Recurrences were treated with chemotherapy in 10 cases and with hormones in 1 case. Seven patients died of progressive serous carcinoma 2 to 5 years after the recurrence. One patient died of leukemia with recurrent ovarian tumor 10 years after the recurrence was detected. Two patients are alive with progressive disease 1 and 7 years after the recurrence, and 1 patient whose disease recurred as a SNLMP is alive with no evidence of disease 9 years after the recurrence. These 11 patients were compared with 16 patients who had stage I ovarian SNLMPs that did not recur after a minimum follow-up of 15 years. There was no difference in the age of the patients, gravidity, size of the tumors, or several microscopic parameters, including degree of epithelial proliferation, number of mitoses, and nuclear atypia. Microinvasion was found in one case. The only significant difference between the two groups was the low frequency of endosalpingiosis in the cases that had no disease recurrences (12.5% versus 72.7%). In summary, we found no clinical or pathologic features that can unequivocally predict the recurrence of stage I ovarian SNLMPs. Because of the long interval to recurrence, the fact that the recurrent tumors in 10 of 11 patients were serous carcinomas, and the result of the X-chromosome inactivation in one case, the recurrent tumors could represent independent primaries or a slow progression of one clone present in the SNLMPs.