Aims: Statistics on drug-related deaths (DRD) provide crucial information on the drug situation. The European Monitoring Centre for Drug and Drug Addiction (EMCDDA) has published a specification for extracting DRD from national mortality registers to be used in international comparisons. However, surprisingly little is known of the accuracy of DRD statistics derived from national mortality registers. This study assesses the accuracy of Swedish data derived from national mortality registers by comparing it with other sources of data. Methods: We compared five Swedish datasets. Three were derived from national mortality registers, two according to a Swedish specification and one according to the EMCDDA specification. A fourth dataset was based on toxicological analyses. We used a fifth dataset, an inventory of DRD in Stockholm, to assess the completeness and coverage of the Swedish datasets. Results: All datasets were extracted from high-quality registers, but still did not capture all DRD, and both the numbers and demographic characteristics varied considerably. However, the time trends were consistent between the selections. In international comparisons, data completeness and investigation procedures may impact even more on stated numbers. Conclusions: Basing international comparisons on numbers or rates of DRDs gives misleading results, but comparing trends is still meaningful.