This follow-up study presents the effects of DES on the genital tract of male and female offspring of mothers who were part of a double-blind, placebo-controlled investigation during 1951 and 1952 aimed at determining the effect of DES on pregnancy. Epididymal cysts, hypotrophic testes, and capsular induration were the more common genital lesions found in 25% of 163 DES-exposed males as compared to 6% in 168 control males. Semen analysis data on 39 subjects of the DES-exposed group and 25 subjects of the control group showed that 26% of the DES-exposed group produced an ejaculate volume under 1.5 ml; no such cases were observed in the control group. The average values for sperm density ant total motile spermatozoa per ejaculate, although in the normal range, were more than two times lower in the DES-exposed group as compared to the controls. A quality score of greater than 10 ("severely pathologic semen") was found in 28% of the DES-exposed group as compared to 0 in the control group. An association of pathologic semen quality with physical abnormalities was found only in the DES-exposed group. Two cases of azoospermia, one without genital abnormalities on physical examination and one with bilateral hypotrophic testes were observed so far in the DES-exposed group. Eighteen percent of 229 DES-exposed female patients had irregular menstrual cycles (oligomenorrhea) as compared to 10% of 136 controls. The history of pregnancy revealed a lower incidence of pregnancy in the DES-exposed group (18%) than in the control group (33%). Circumferential ridges of the vagina and cervix were seen in 40% of 229 DES-exposed females but in none of 136 controls. Colposcopic findings in the vagina revealed adenosis in 66.8% of the DES-exposed females and in 3.6% of the control group. Dysplastic lesions were more prevalent in the vagina and cervix of the DES-exposed subjects. No cases of cancer were observed in either the male or female offspring.