CONTEXT AND OBJECTIVE: Pap smears are the most common and inexpensive screening method for cervical cancer. We analyzed micronucleus prevalence in exfoliated cervical mucosa cells, to investigate associations between increased numbers of micronuclei and risk factors for cervical cancer. DESIGN AND SETTING: Analytical cross-sectional study, at Instituto de Pesquisa em Oncologia (IPON). METHODS: Exfoliated cervical cells were obtained from 101 patients between September 2004 and November 2005. Patients' ages, habits (passive or active smoking, alcoholism and numbers of sexual partners), age at first sexual intercourse, contraceptive methods used, histories of sexually transmitted diseases, use of hormone replacement therapy, numbers of pregnancies and abortions, inflammatory cytology and cervical intraepithelial neoplasia (CIN) were obtained. Cells were collected using Ayre spatulas, transferred to vials containing 0.9% saline solution for micronucleus tests and analyzed at 1000x magnification. The number of micronuclei in 1,000 epithelial cells per patient sample was counted. RESULTS: Comparisons between groups with active (7.9 ± 7.8) and passive (7.2 ± 10.6) smoking versus no smoking (3.7 ± 5.1); with/without alcoholism (7.8 ± 1.4 and 6.9 ± 10.1); with/without inflammatory cytology (10.7 ± 10.5 and 1.3 ± 1.7); and with CIN I, II and III and no CIN (respectively 4.3 ± 4.3, 10.6 ± 5.3, 22.7 ± 11.9 and 1.3 ± 1.4) found elevated micronucleus prevalence (P < 0.05). CONCLUSIONS: We concluded that the prevalence of micronuclei in exfoliated uterine cervical cells was greater in patients with one or more risk factors for uterine cervical cancer than in patients without risk factors.