In a retrospective review of 6706 pregnancies between 1981 and 1985, uterine leiomyomas were documented by antenatal sonography in 93 (1.4%) patients. The obstetric records and sonograms of patients with documented leiomyomas were reviewed and compared with data from matched control patients managed at our institution during the same time period. Among the 93 patients with leiomyomas, 14 (15.1%) had one or more leiomyomas subjacent to the maternal surface of the placenta. Significantly, eight of 14 (57%) of these patients with retroplacental leiomyomas subsequently developed abruptio placentae, which resulted in the deaths of four fetuses. Conversely, among the remaining 79 patients whose leiomyomas were not retroplacental, abruptio placentae occurred in only two patients (2.5%), neither of which resulted in fetal death. Clinically significant pain requiring narcotic analgesia developed in 14 of 93 (15.1%) patients and premature labor occurred in 20 of 93 (21.5%); pain and premature labor correlated positively with the size of the largest myoma. Delivery by cesarean section and vacuum assistance occurred significantly more frequently in patients with leiomyomas than in those without documented leiomyomas. In this population uterine myomas did not significantly alter the incidence of intrauterine growth retardation and low Apgar scores.