The National Cooperative Diethylstilbestrol Adenosis (DESAD) Project has completed the major portion of its enrollment phase with the examination of more than 3000 daughters of women taking synthetic nonsteroidal estrogens (denoted DES) during pregnancies occurring from the early 1940s to the mid-1960s. The aims of the Project are to fill urgent needs for information on the prevalence and incidence of structural and epithelial abnormalities or neoplastic changes and their complications in these young women. Participants are grouped by mode of entry as identified by prenatal record review (40.1%), documented as DES-exposed but walking in (25.1%), or referred (22.8%) to the DESAD Project for examination, and not documented as exposed but having gynecologic abnormalities typical of those associated with DES exposure (12.0%). This study cohort, in part having paired controls, will be examined annually for at least 5 years. Details of the design and selected preliminary findings are reported.