Although screening for human T-cell lymphotropic virus types I and II (HTLV–I/II) antibodies in volunteer blood donors has been systematic in Greece since 1995, the epidemiology and the determinants of HTLV-I/II infection are not well defined among population groups. During 1997–2005, the prevalence of HTLV-I/II infection was investigated in a sample of 2016 pregnant women, 102 multitransfused haematologic and oncologic patients, 93 thalassaemic patients and 57 intravenous drug users originating from four geographic areas of Pelopennese peninsula, Greece. One recipient of HTLV-I infected blood and the relatives of a woman died from adult T-cell leukaemia/lymphoma (ATTL) related to HTLV-I have also been tested. The subjects were initially screened by an enzyme immunoassay whereas Western blot, INNO-LIA HTLV, polymerase chain reaction and nucleotide sequencing confirmed the infection. One thalassaemic patient had proved HTLV-I infection giving an overall prevalence of 11 per 1000. In the recipient of the infected blood and in two of the five relatives of the woman died from ATTL, HTLV-I infection was also detected. In none of the pregnant women, multitransfused patients and intravenous drug users HTLV-I/II infection was confirmed. These data suggest that HTLV-I is present in Greece among populations at high-risk. However, they would not support the need for HTLV-I/II antenatal screening in Greece.