Persons with a history of injection drug use have many risk factors for the development of chronic venous insufficiency (CVI), yet this phenomenon has not been studied systematically in this population. Persons (N= 204) with a history of injection drug use who were in enrolled in a treatment center were examined for clinical manifestations of CVI. The CVI clinical classification was graded on a 7-point scale for each leg. Most participants (n=179, 87.7%) exhibited clinical evidence of CVI. Significant predictors of CVI clinical manifestations were leg infections/cellulitis (p=.53); years injection in the veins of the groin, legs, and feet (p=.47); deep vein thrombosis (p=.37); and total years injection heroin (p=.27). There was a linear functional relationship between years of injection drug use and the CVI clinical classification, but only when the injections were in the veins of the groin, legs, or feet; otherwise, the specific mechanisms of this relationship were not evident. The findings indicate that CVI is a common occurrence in persons who have injected drugs. (C) 2001 John Wiley & Sons, Inc.