Increased cardiovascular risk have been reported in heroin abuse. It has been suggested that multiple mechanisms may be involved in the relationship between heroin abuse and cardiovascular risk; these include hypoxia, vasculitis and vasospasm. In some studies increased platelet aggregation and morphological changes have also been reported in heroin addicts. Mean platelet volume (MPV) is an indicator of platelet reactivity and it plays an important role in the pathophysiology of cardiovascular diseases. The aim of this study was to investigate MPV values in heroin addicts. We measured serum MPV values in heroin addicts and control subjects. MPV was significantly higher among heroin addicts than in the control group(8.6+/-1.1 vs. 7.8+/-0.7 fL respectively; p<0.001). In correlation analysis, there was correlation between duration of heroin use and MPV (r:-0,09 p:0.32). We have found that MPV was elevated in heroin addicts.