This paper reports the clinical and virologic results of CO2 laser treatment for squamous intraepithelial lesions in 154 patients. On the basis of cervical canal involvement, vaporization or conization was performed. Failure rates following the first and second treatments were 4.5% and 0%, respectively. However, human papillomavirus persistence in several women with completely normal follow-up suggests that one of the possible mechanisms of failure could be reexposure of the healing area to a viral reservoir within the "normal" epithelium.