Ten serous neoplasms of low malignant potential (LMP) resected during pregnancy were found in the files of the University of Texas M. D. Anderson Cancer Center (UTMDACC). Microscopically, all tumors had marked epithelial proliferation with abundant eosinophilic cells, and eight had intraluminal mucin. Multiple areas of microinvasion were found in eight cases. Additional unusual features were found in three cases. One patient presented with a serous LMP tumor in a supraclavicular lymph node. After resection of an ovarian serous LMP tumor, she was treated with chemotherapy and is without evidence of disease after 21 years. One patient had tumor resected at 24 weeks of gestation and at 2 months postpartum. Marked regression of the epithelial proliferation, the number of eosinophilic cells, and the amount of mucin was seen in the second specimen. Another patient had multiple peritoneal nodules at cesarean section, one of which was biopsied and diagnosed as a primary serous LMP of the peritoneum with multiple areas of microinvasion. Two months later a diagnostic laparoscopy was performed and no residual disease was found. All patients are alive with no evidence of disease. In summary, serous LMP tumors during pregnancy have microscopic and clinical features suggesting aggressive behavior; however, these features appear to regress at the termination of the pregnancy.