This survey started in May 1989 and deals with 2,436 patients treated by 10 gynecologists from the Brussels region. In addition to routine cytological analysis in cervical smears, an additional test for Human Papilloma Virus (HPV 16, 18 and 33) was advised for these women. Gynecologists filled in a questionnaire about these patients. In cases with benign cytology, virus prevalence was 2 times greater in woman who took contraceptive pills, over at least 6 months, than in each of the other groups using either diaphragm or male condoms or no contraception, or at menopausal age. It was strange to find that viral prevalence varied according to the pill trade mark, but not according to the pill hormonal content. No confounding factor in population recruitment could be detected. In contrast to viral infection, prevalence of cancer lesions was not increased in the oral contraception group. Squamous intraepithelial lesions of Low Grade and High Grade (SIL LG and HG) were on the contrary 2 times less frequent in women taking the pill, with or without HPV infection. During follow-up of 223 women, the same HPV genotype persisted in SIL lesions but it disappeared within 4 to 8 weeks in 68% of normal cervical smears. However, beyond this period, the proportion of women with persisting virus remained nearly constant, indicating that a subgroup may be less able to mount a defence against the infection. Risk factor of cigarette smoking for SIL LG or HG was 1.6 in women with HPV and 4.0 in those with no virus. This factor was 3.3 in women with oral contraception and 4.5 in the other group.