The anatomic, colposcopic, cytologic, and histologic findings of the cervix in 300 women exposed to diethylstilbestrol (DES) in utero are reported. Structural cervical abnormalities were found in 51.7% of these patients and an abnormal colposcopic examination was present in 50.6%. The initial interpretation of the pathologic specimens revealed that 26.6% of patients had cytologic or histologic evidence of cervical dysplasia. A uniform pathologic review demonstrated that 10.8% of the cytologic specimens and 37.5% of the histologic specimens had been overread by the initial pathologist. A correlation of the review cytology and histology revealed that the Papanicolaou smear sensitivity for the prediction of abnormal histology was 83.9% and specificity was 86.3%. The probability of an atypical cytologic finding predicting an abnormal histologic pattern was highly significant (P less than .00001). Colposcopic and structural cervical abnormalities were not predictive of an abnormal histologic diagnosis. Of the 18 patients (6%) with histologic evidence of mild-moderate dysplasia, 12 have been followed with no treatment, and cytologic and colposcopic examination has been normal. Marked dysplasia-carcinoma in situ was found in 14 patients (4.7%). Their therapy is summarized. These data strongly suggest that women exposed to DES may be followed safely with Papanicolaou smears and colposcopic examinations provided that both cytopathologists and colposcopists are cognizant of the metaplastic changes in the DES progeny that distinguish them from patients with cervical intraepithelial neoplasia (CIN) who were not exposed to DES. Biopsy should be performed only if indicated by cytologic atypia, colposcopic evidence of advanced CIN, or the presence of an invasive lesion.