A survey was performed on literature on medicinal drugs and traffic safety, mainly published 1991 or later. Results from epidemiological and experimental studies were covered. Epidemiological studies are of different types. Drug prevalence is studied in drivers suspected of driving under the influence of alcohol or drugs or in drivers injured in traffic accidents. Studies of drug prevalence in the general driving population are less common. These studies do not permit calculations of accident risks. The second type of epidemiological studies is accident analysis studies, where accident risks are calculated for different drugs. These studies can be divided into case-control studies, responsibility studies and pharmaco-epidemiological studies. Because of a number of methodological problems in these studies, the results must be interpreted with caution. The experimental studies are limited to those performed in real car driving or in driving simulators.