Among women exposed in utero to diethylstilbestrol (DES) and enrolled in the Diethylstilbestrol Adenosis (DESAD) Project, structural anomalies of the cervix or vagina were found in 25% of the 1,655 subjects identified by review of prenatal records, 43% of the 800 who themselves requested entry into the project, and 49% of the 1,089 referred by physicians but in only 2% of the 963 control subjects. Among the 367 cases found by record review to have complete information on the DES exposure, multivariate analysis indicated close association of the anomalies with the gestational week of first exposure and the total dose. Also, the prevalence rate of the anomalies was lower among subjects who had been pregnant and higher among those with later age at menarche.