To estimate the impact of intravenous drug use (IVDU) on mortality in the general population of young adults in Rome, Italy, the Population Attributable Risk (PAR) was calculated for the overall and cause-specific mortality in the 15-34 years age group. Relative risks were derived from a previous historical cohort study on mortality among 4200 intravenous drug users (IVDUs) in Rome, in which increased mortality from cardiovascular, respiratory, and gastrointestinal diseases as well as from violence, overdose and AIDS had been observed. The prevalence of the risk factor (i.e. the proportion of IVDUs) in the general population was estimated using the 'multiplier formula' and 'capture-recapture' methods. The proportion of all deaths attributable to IVDU in the 15-34 age group in the Roman population was 16% and 9% in males and females, respectively. The cause-specific attributable proportions were 66% for endocarditis and 37% for cirrhosis in males, and 36% for endocarditis and pneumonia in females. These findings further document the relevant health consequences of IVDU on the general population of a large metropolitan area.