The prevalence of markers for human immunodeficiency virus types 1 and 2 (HIV-1, HIV-2), human T-lymphotropic virus type I (HTLV-I), hepatitis B virus (HBV) and hepatitis C virus (HCV), and cytomegalovirus (CMV) was evaluated in a population of 305 multiply transfused thalassemia patients in Belgium, France, and Italy (Sicily). No patients were found positive for HIV-2 antibodies. Two French patients were seropositive for HIV-1, having been infected before systematic blood screening. Antibodies to HTLV-I were found in two Sicilian patients. A positive anti-HCV enzyme-linked immunosorbent assay was found in one-third of the patients and a positive CMV IgG test in two-thirds. Twenty-two percent of the patients in the three countries were uninfected by HBV and were not vaccinated. With the exception of HIV-1, HIV-2, HTLV-I, and anti-hepatitis B surface antigen assays, all markers were encountered more frequently in Sicilian patients than in French or Belgian patients. This study emphasizes the need to improve HBV vaccination coverage in the three countries. At present, data indicate that the introduction of routine screening for HTLV-I should be considered, particularly in Sicily.