Objective: To assess the seroprevalence and risk factors for HTLV-I infection in Peruvian women. Methods: Five hundred and sixty-eight healthy women >20 years of age from three Peruvian regions were randomly selected and screened for HTLV-I. ELISA-reactive sera were confirmed via immunofluorescence assay, recombinant immunoblot assay, Western blot, and PCR. Women from Huanta (n = 303), an Andean city inhabited by indigenous Quechuans, El Carmen (n = 132), a primarily African-American coastal town, and Lima (n = 133), with its Mestizo population, were selected. Results: HTLV-I antibodies were present in 2.5 % (14/568) of women (1.3 % in Huanta, 3.8 % in El Carmen, and 3.8% in Lima); 2.5%, 2.7% and 2.6% of Quechuans, Mestizas and African-Americans, respectively, were infected. History of a blood transfusion (P<0.00002), chronic scabies (P<0.02), having a relative with leukemia (P<0.04), age ±38 years (P<0.03), young age at first intercourse (P<0.04), lifetime partners >4 (P<0.04) educational status (P<0.02) and >4 pregnancies (P<0.03) were significantly associated with infection. Conclusions: HTLV-I is endemic among asymptomatic Peruvian women. Parenteral, vertical and heterosexual transmission are associated with infection.