Screening examinations of 34 females, 13 to 24 years of age, who had been exposed to stilbestrol in utero revealed vaginal adenosis, characterized by epithelium resembling that of the endocervix, endometrium and uterine tube, in 13. Transverse cervical or vaginal ridges (partial septa) were found in 7 patients. With one exception, all patients with ridges also had adenosis. Cervical erosion was detected in 21 females, including all of those with adenosis. The dose of stilbestrol administered to mothers of patients with adenosis or ridges ranged from 10 mg daily to doses that gradually increased throughout pregnancy. Treatment was started before week 12 of gestation. The congenital origin of the observed changes is discussed, and the importance of screening and follow-up examinations of exposed patients is stressed.