Cohort study on 471 subjects resident in the metropolitan area of Bologna who had visited a public treatment center for problems due to the abuse of cocaine from January 1, 1988 to December 31, 2009. Two user typologies were created: cocaine users (no heroin) and heroin and cocaine users. Crude mortality rates and standardized mortality ratios were calculated. We performed a regression analysis using the Poisson method. The study results show a higher mortality risk for those injecting substances and for subjects who took both heroin and cocaine. They appear to have different characteristics from their counterparts who do not use heroin. Future studies should be oriented to this aspect.