There is some evidence that a significant proportion (12%) of women, prospectively followed after negative cervical cytologic findings, develop tissue-proven high grade squamous intraepithelial neoplasia (HSIL) within a short period (up to 24 months). The present study was undertaken to address the validity of this statement since such a high prevalence of spontaneous HSIL, if true, may challenge the value of an annual cervicovaginal cytologic smear examination. Cytologic smears collected from 82 patients with tissue-proven HSIL and obtained in the preceding 24 months were evaluated. The vast majority (90%) of these smears revealed evidence of cervical epithelial abnormalities prior to the development of HSIL-88% at 24 months and 96% at 12 months. The cytomorphologic features of low grade squamous intraepithelial neoplasia were observed in 45% of the smears, while the remaining cases were not normal or negative but had cytologic evidence of human papillomavirus (HPV)-associated changes (described elsewhere), including binucleation and multinucleation, epithelial plaques and pearl formations, and hyperkeratosis, dyskeratosis and parakeratosis. Persistent negative cytology was found in only three cases. Although these HPV-related cellular changes may not have an independent predictive value for HSIL, our study demonstrated that their awareness and detection can help to identify women at risk of potentially more advanced lesions. Thus, an annual cytologic smear examination is valuable and accurately reflects the presence of HPV-associated epithelial changes and precursor lesions of HSIL.