The objective was to examine the prevalence of human papillomavirus (HPV) DNA infection in mild cervical dysplasia and to evaluate longitudinally the persistence of HPV DNA positivity in an observational study, aiming at identifying the role of peripheral blood lymphocyte natural killer activity in the natural history of dysplastic disease. Twenty-three patients with histologically proven mild cervical dysplasia were selected. The HPV DNA positivity, determined by polymerase chain reaction, and cervical dysplasia were monitored cytologically and colposcopically at the 3rd (time 1), 6th (time 2) and 12th months (time 3), and defined by biopsies for routine histology taken at times 2 and 3. For each patient included in the study, the immune reactivity was evaluated at the time of diagnosis and afterwards, longitudinally during the follow-up. The immune status analysis included T lymphocyte subsets (CD3, CD4, CD8, CD56, CD 16 monoclonal antibodies by Beckton Dickinson, Mountain View, Calif., USA) and determinations of natural killer cell activity (against the sensitive cell line K 562). Eighteen out of the 23 women with mild cervical dysplasia (78.3%) were found positive for HPV DNA, with a significantly high representation of HPV DNA type 16 (55.6% of cases). At the end of the study, 12 out of 18 HPV-DNA-positive women became negative (defined by two or more negative tests) for the original HPV DNA type, with 66.7% of spontaneous HPV DNA negativization rate (p = 0.6). In 83.3% of the women with definitive HPV DNA negativization and in 7.5% of those with a constant HPV DNA negativity, the resolution of HPV DNA infection was associated with a clinical-pathologic remission of the lesion. Patients with spontaneous HPV DNA negativization and/or clinical-pathologic resolution of cervical dysplasia had a significantly higher mean value of natural killer activity than those with persistent disease. No significant modifications were observed with respect to lymphocyte subsets. The longitudinal evaluation of natural killer activity showed constantly low values of natural cytotoxicity in patients with persistent dysplasia, while women with regressive lesions had a significant increase in immune reactivity during the follow-up. The majority of patients with mild HPV-DNA-associated dysplasia can be followed with confidence and with the expectation that the minimal degree of dysplasia will eventually disappear. The evaluation of natural cytotoxicity is a useful parameter of functional immune status, correlated with the natural history of the disease.