A new colposcopic sign (sharpness of peripheral margins) was graded into three objective categories representing subclinical papillomaviral infection, lower grade dysplasia, and grade 3 cervical intraepithelial neoplasia. Colposcopic features were prospectively recorded in 72 women and then correlated with histologic findings. Histologic diagnoses were evenly spread within the disease spectrum: 18 patients had subclinical papillomaviral infection without associated dysplasia; 15 had grade 1, 16 had grade 2, and 23 had grade 3 cervical intraepithelial neoplasia with or without koilocytotic atypia. Differences in the pattern of the peripheral margin were discriminatory throughout the entire diagnostic range. Predictive accuracy of this new colposcopic sign (79%) compared favorably with that of color (72%), vascular atypia (81%), and iodine staining (72%). Each criterion was independent of the other three. Hence, combining these four individual signs into a colposcopic index was 97% correct in forecasting approximate histologic findings. Because formulation of the colposcopic index is based on critical analysis rather than pattern recall, the use of this method will greatly simplify the otherwise arduous task of learning colposcopy.