The present investigation analyzes the characteristics of traffic accidents involving psychiatric patients and comprises all persons who during the period 1970-74 have been admitted to a psychiatric in-patient institution and who during the period 1972-74 have been involved in a traffic accident causing bodily injury. Accidents with psychiatric patients involved constitute about 5.7% of all traffic accidents reported in Denmark. Compared with the total group of accidents, they are characterized by an over-representation of women and of persons in the age group 25-54 years. Accidents with psychiatric patients are over-represented during the period July-September, and in areas densely built up. The accidents tend to be more complicated, and the psychiatric patients are more likely to get injured and be hopitalized due to the accident. The investigation is based exclusively on routinely collected data. The limitations with which the results are encumbered and the problems concerning methodology and comparison of different studies are discussed.