Human T-cell lymphotropic virus type I (HTLV-I) is a unique retrovirus associated with specific malignancies of T cells in humans. The virus is endemic to Japan, the Caribbean, Africa, and the southeastern United States. We report here the first case of HTLV-I-associated lymphoma in an atypical host. The incidence of antibodies in this individual with a T-cell malignancy strongly suggests HTLV-I virus as the causative agent. Direct identification of viral DNA using an HTLV-I-specific probe provides definitive evidence of infection.