There still is no cure for the acquired immunodeficiency syndrome (AIDS). Its etiologic agent is the human immunodeficiency virus (HIV), and transmission occurs through sexual relationships, contacts with blood, and vertically (mother to child). In this study, we sought to determine the prevalence of HIV among blood donors at a blood bank in Curitiba. We studied 213,666 blood donations made from March 1, 1992, to April 25, 1999. Each potential blood donor first answered a questionnaire, submitted to a clinical examination, and filled out a self-exclusion card. Blood was collected and analyzed only from the candidates approved by the first two criteria. Two tests were used to detect HIV: ELISA for screening, and Western-Blot for confirmation. The results were analyzed statistically by determining the 95% confidence interval. Of the total number of donors, 156,942 were men, and 56,724 were women. There were 319 cases of HIV infection (244 men, 75 women). There were no significant differences between genders, or among the different age groups, or between first-donation and repeated-donation donors. There was a significant predominance of HIV infection among single individuals compared to married, widowed, and other individuals. The same occurred among married and divorced individuals compared to widowed subjects. The prevalence of HIV among blood donors was 0.149% (0.155% among men and 0.132% among women). The frequency of HIV was statistically identical among new blood donors and repeat donors. A large number of HIV-infected married women was also observed.