In most parts of Europe only a limited number of sporadic cases of HTLV-I infections have been identified. So far, the few cases found in Germany have always been linked to individuals with relations to endemic areas. Here we report the first HTLV-I infection from a German ATL patient without any known risk for HTLV-I infection and with no relations to known endemic areas. The DNA sequence of the provirus was determined, and a phylogenetic analysis based on the LTR sequence established a close relationship with HTLV-I sequences previously found in two Romanian patients. Our data suggest the existence of a previously unrecognized cluster of HTLV-I infections in southeastern or central Europe.