Objective: The human T-cell leukemia/lymphoma virus type I (HTLV-I) is an etiologic agent of adult T-cell leukemia/lymphoma and tropical spastic paraparesis. One of the major routes of transmission of the virus is through blood transfusion. The aim of this study was to determine the prevalence of HTLV-I infection in volunteer blood donors in Kuwait. Methods: A donation of 97,602 blood units in Kuwait from March 1995 to October 1997 was tested for antibodies against HTLV-I and related virus (HTLV-II). The testing was carried out in three steps: first screening by enzyme immunoassay (EIA) for anti-HTLV-I/II, second testing of initially positive samples by the EIA and final confirmation of true positives by Western blot. Results: Twenty-one HTLV-I-positive donors have been identified (7 Kuwaitis, 5 Indians, 4 Iranians, 2 Bedouins, 1 Omani, 1 Egyptian and 1 Filipino). None of the EIA-reactive samples was positive for HTLV-II by Western blot. The frequency of HTLV-I-positive blood donations was: 1:4,648 and the infection was significantly more prevalent among Indians and Iranians. Conclusion: The prevalence of HTLV-I infection in blood donors in Kuwait is one of the highest in the world and compulsory screening of blood for HTLV-I is fully justified.