Driver sleepiness is believed to be a strong contributing factor to road traffic crashes. Acute sleepiness risk factors, such as driving during early morning hours or having insufficient sleep, was observed in 15% to 25% of the car crash injuries in New Zealand. Most studies are observational and describe the information about the crashes, whereas controlled studies are rare. One exception is the study by Connor et al. (2002), which used a case-control design and compared 571 car drivers involved in crashes (in which at least one driver was admitted to hospital or killed - "cases") with 588 representative drivers (controls) recruited while driving on public roads. The results showed a strong association between indicators of acute sleepiness and the risk of an injury crash, whereas measures of chronic sleepiness showed no association with injury risk. The aim of the present study was to carry out a similar study in Sweden and examine the relationship between acute and chronic sleepiness characteristics, including disturbed sleep and other factors that may contribute to driver sleepiness, with the risk of crashes in which the driver was admitted to hospital.