Two hundred twenty-eight adnexal masses during pregnancy were discovered among 37,159 deliveries occurring between January 1, 1983 and October 31, 1988 at Kapiolani Medical Center for Women and Children in Honolulu. Hydatid cysts of morgagni (45.6%) occurred most frequently, followed by benign cystic teratomas (15.8%), epithelial cystadenomas (15.4%), and paraovarian cysts (13.6%). There were no malignant or borderline tumors. The patients were categorized as 22.1% part Hawaiian, 18.5% white, 17% Filipino, and 16% Japanese. We demonstrated an increased incidence of benign cystic teratomas in Filipinas (P< .01). There was no significant predisposition for the occurrence of non-neoplastic or other neoplastic lesions among any of the other ethnic groups studied.