Infection with human T-cell lymphotrophic virus-I (HTLV-I) is now a global epidemic, affecting 10 million to 20 million people. This virus has been linked to life-threatening, incurable diseases: adult T-cell leukemia/ lymphoma (ATLL) and HTLV-I-associated myelopathy/ tropical spastic paraparesis (HAM/TSP), The cumulative lifetime risk of developing these incurable diseases is approximately 5% in asymptomatic patients. For the emergency physician practicing among patients from high-risk groups, HTLV-I and its associated diseases are presenting an increasing challenge. This report describes its transmission, seroprevalence, treatment, and methods of controlling spread of this retrovirus, Coinfection with HTLV-I and HIV has been shown to accelerate the progression of acquired immune deficiency syndrome (AIDS), (C) 2000 Elsevier Science Inc.