The epidemiology of HTLV‐I infection in female prostitutes was studied in a survey of 395 prostitutes from Callao, Peru (the port city of Lima), 72 prostitutes from Iquitos, Peru (another port city on the Amazon River), and 510 prenatal clinic patients from Lima. Prostitutes reported a mean of 8.8years (range, 1–39 years) of active prostitution and a mean of 205 sexual contacts during the month prior to the study. The percentage of prostitutes with HTLV‐I antibody (21.8%) was significantly higher than patients attending a prenatal clinic (3.1%; P < .0001). The prevalence of HTLV‐I antibody increased steadily with age in prostitutes, but no age trend was noted i n prenatal patients. By multiple logistic regression analysis, an independent association was found between HTLV‐I seropositivity and a history of prostitution i n Callao, age, and positive syphilis serology when all 977 study subjects were evaluated. When prostitutes alone were analyzed, the number of years of exposure as a practicing prostitute was associated with HTLV‐I seropositivity after controlling for age. These data indicate a greatly increased risk of HTLV‐I infection in prostitutes in Callao, Peru, and suggest an association between sexual activity and HTLV‐I transmission. © 1992 Wiley‐Liss, Inc. Copyright © 1992 Wiley‐Liss, Inc., A Wiley Company