The aim of this study was to evaluate the long-term efficacy of beta-interferon treatment in the management of cervical intraepithelial neoplasia associated with human papillomavirus (HPV) infection in a selected group of patients. Thirty-nine patients who had histologically proven cervical intraepithelial neoplasia I or II with concurrent HPV infection were administered 27,000,000 IU of intramuscular beta-interferon. Periodical controls were carried out based on Papanicolaou smears and/or colposcopic examination and DNA HPV determination was performed by hybridation test, for a maximum of 8 years' follow-up. An initial complete response rate of 75% was obtained, with a recurrence rate of 25%, cervical intraepithelial neoplasia with late manifestation was of higher grade. Treatment interruption due to side-effects was not necessary. Associated viral infections appeared to be a recurrence risk factor, but not smoking or parity. While immunomodulatory treatment with beta-interferon has good long-term results in cervical intraepithelial neoplasia I/II treatment, wider randomized studies are required to obtain conclusive results.