Theca lutein cysts are benign neoplasms known to be associated with twins, molar pregnancy and erythroblastosis fetalis, but they are only rarely associated with a normal singleton pregnancy. Their natural course is postpartum spontaneous regression. Documented cases were noted because of abdominal pain or dystocia. This paper reports theca lutein cysts which were asymptomatic and were first noted ultrasonographically in a singleton gestation at term. In a few published cases and in a larger number of unpublished cases, apparent confusion as to the benign nature of these cysts has led to unwarranted bilateral oophorectomy. Asymptomatic theca lutein cysts undoubtably occur more commonly than they are reported. With the increasing use of ultrasonography and cesarean section, this condition probably will be observed more frequently in the future. At the time of laparotomy in late pregnancy with ovaries which appear pathological, tissue biopsy and evaluation is of critical importance in order to avoid unnecessary castration in this group of young women.