This study examines the quality of street heroin seized in Vienna in 1999 and whether there was a relationship between the purity of street heroin and the number of heroin‐related emergencies as well as the number of heroin‐related deaths. Street heroin confiscated by the Viennese police, run‐sheets of drug‐related emergencies, and postmortem reports of drug‐related deaths in Vienna in 1999 were analyzed. A total of 415 retail samples with a total weight of 128.02 g contained a median percentage of 6.5% diacetylmorphine (range: 0.0–47.0%). All the samples contained a diluent, mainly lactose, as well as adulterants, such as caffeine and/or paracetamol. During the study period, 75 heroin‐related deaths and 387 heroin‐related emergencies were registered in Vienna. Time‐series analysis revealed no statistically significant relationship between the rate of heroin‐related incidents and the diacetylmorphine concentration of street heroin samples confiscated in Vienna in 1999. The widely held belief that the number of heroin‐related deaths could be explained simply through fluctuations in the purity of street heroin could not be substantiated, even though the results of this study do not rule out an association between the purity of heroin and heroin‐related deaths/emergencies.