Objective: A prospective study was conducted to determine the prevalence of human T-cell lymphotropic virus type I (HTLV-I) infection among healthy Japanese migrants and their descendants in Peru. Methods: A total of 407 persons were enrolled at the Peruvian-Japanese Medical Center in Lima during routine visits for health evaluations. Each study volunteer was interviewed to obtain clinical and epidemioiogic data, and a blood sample was obtained for HTLV-I testing. Sera samples were initially tested for antibody by enzyme-linked immunosorbent assay'(ELISA). All ELISA reactive sera were further tested by Western Blot assay, and the results were recorded in accordance with the manufacturer's recommendations. Results: Among the 407 study volunteers, HTLV-I infection was demonstrated in 6.8% (19/280) of females and 3.2% (4/127) of males. Infection rates significantly increased with age, with 28.5% of volunteers over 80 years of age being positive (P < 0.05). The migrants from Japan had the highest infection rate (15.8%), whereas none of the second generation volunteers were positive (P < 0.05). The incidence among those with ancestors from Okinawa was 9.3%, and for those with ancestors from the central zone of Japan, 1.2% (P < 0.05). Conclusions: These data indicated that HTLV-I infection rates were highest among the older volunteers from Okinawa and Kyushu, and that evidence of infection was not found among their offspring.