This study documents the costs of heroin addiction in the United States, both to the addict and society at large. Using a cost-of-illness approach, costs were estimated in four broad areas: medical care, lost productivity, crime, and social welfare. We estimate that the cost of heroin addiction in the United States was US$21.9 billion in 1996. Of these costs, productivity losses accounted for similar to US$11.5 billion (53%), criminal activities US$5.2 billion (24%), medical care US$5.0 billion (23%), and social welfare US$0.1 billion (0.5%). The large economic burden resulting from heroin addiction highlights the importance of investment in prevention and treatment. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.