OBJECTIVE To evaluate colposcopically directed brush cytology as a substitute for directed biopsy of acetowhite lesions identified during pregnancy. METHODS Pregnant patients eligible for the study were referred for colposcopic evaluation for either newly diagnosed abnormal cervical cytology or follow-up of a previously diagnosed squamous intraepithelial lesion (SIL). All patients with acetowhite lesions underwent colposcopically directed brush cytology followed by directed biopsy. RESULTS Of 81 pregnant patients referred, 50 paired samples of colposcopically directed brush cytology and directed biopsies were evaluated from 49 patients. One patient was sampled in the first and third trimesters and one patient's brush cytology was unsatisfactory for interpretation because of clumping artifact, leaving 49 brush-biopsy pairs that were satisfactory for examination. One patient in the study group had an intrauterine fetal death of uncertain cause, remote from the time of biopsy. Compared with the corresponding biopsy, the directed brush caused significantly less blood loss (P < .001). For all diagnostic categories, directed cytology demonstrated a good degree of correlation with biopsy (kappa = 0.73). The brush technique correctly identified 12 of 14 cases (86%) of biopsy-proved cervical intraepithelial neoplasia II-III as high-grade SIL. If one considers "atypical squamous cells, favor human papillomavirus effect" as a true positive, brush sensitivity was 88 +/- 9% and specificity was 74 +/- 12%, with an accuracy of 80%. CONCLUSIONS In the absence of lesions suspicious for carcinoma, colposcopically directed brush cytology is a safe substitute for directed biopsy in pregnant patients.