An analysis of 6055 colposcopically directed biopsy specimens from 2635 diethylstilbestrol (DES)-exposed women and 445 biopsy specimens from 277 nonexposed women was undertaken to correlate microscopic findings with colposcopic patterns. All examinations were performed using a standardized protocol which required that each participant have colposcopy, cytologic smears, and biopsy of abnormal colposcopic lesions. The findings of colposcopic "columnar epithelium, gland openings, and Nabothian cysts" correlated most often with glandular epithelium in the biopsy specimen. "White epithelium," which includes three related colposcopic patterns, mosaicism, punctation, and white epithelium, was associated most frequently (82-93% of cases) with squamous metaplasia, but occasionally with dysplasia and carcinoma in situ (CIS)(0-6%). The presence of dysplasia or CIS in any individual biopsy specimen occurred most frequently with the observation of higher graded lesions by colposcopy or a prior diagnosis of dysplasia.