Human T cell lymphotropic virus type I (HTLV-I) is sexually transmitted. The purpose of this study was to determine the prevalence and risk factors for cervical shedding of HTLV-I DNA among Peruvian sex workers. HTLV tax DNA was detected in cervical specimens from 43 (68%) of 63 HTLV-I-infected sex workers and in samples obtained during 113 (52%) of 216 clinic visits between 1993 and 1997. Detection of HTLV DNA was associated with the presence of ≥30 polymorphonuclear cells (PMNs) within cervical mucus per 100X microscopic field (odds ratio [OR], 4.3, 95% confidence interval [CI], 1.8-10.1) and with the presence of cervical secretions (OR, 2.0; 95% CI 1.2-3.4). Hormonal contraceptive use (OR 1.7; 95% CI, 0.8-3.6) and concomitant cervical infection by Chlamydia trachomatis (OR, 1.5; 95% CI, 0.3-4.3) or Neisseria gonorrhoeae (OR, 1.1; 95% CI, 0.6-3.7) were not significantly associated with HTLV-I shedding. Our results suggest that cervicitis may increase cervical HTLV-I shedding and the sexual transmission of this virus.