OBJECTIVE Our purpose was to evaluate the proliferative activity of cervical intraepithelial neoplasia lesions in human immunodeficiency virus-seropositive women. METHODS The proliferative activity of cervical intraepithelial neoplasia lesions was measured by nucleolar organizer regions-associated proteins count. Twenty-two biopsy specimens of cervical intraepithelial neoplasia lesions from patients positive for human immunodeficiency virus were compared with 22 matched biopsy specimens obtained from controls negative for the virus. RESULTS The mean count of nucleolar organizer regions-associated proteins per cell was 9.5 +/- 3.7 (SD) in human immunodeficiency virus-positive patients and 7.6 +/- 2.8 in human immunodeficiency virus-negative controls (p < 0.0001 by Poisson test of heterogeneity of counts). The difference in counts between the two groups, which was confirmed by log-linear analysis, persisted within each severity stratum of cervical intraepithelial neoplasia and was independent of associated human papillomavirus infection. In human immunodeficiency virus-positive patients log-linear analysis showed that high-grade cervical intraepithelial neoplasia, the presence of human papillomavirus infection, and the severity of human immunodeficiency virus disease were independently correlated with increased nucleolar organizer regions-associated protein counts per cell. CONCLUSIONS The results of this study indicate that the proliferative activity of cervical intraepithelial neoplasia lesions of human immunodeficiency virus-positive patients was increased compared with matched lesions from human immunodeficiency virus-negative women. This finding suggests the possibility of an increased oncogenic progression of cervical intraepithelial neoplasia lesions in human immunodeficiency virus-positive patients.