All autopsied car drivers (n = 480) aged ≥18 years, who were fatally injured and died within 3 days of the crash in northern Sweden over a 13-year period were studied. A grading system was developed to assess the probability of contribution of intrinsic medical factors to the crash. This system takes into account both the risk of sudden incapacitation (inability to cope), based on intrinsic medical factors revealed in the medical history and at autopsy, and extrinsic non-medical contributing factors. Almost one quarter of the drivers were found to have intrinsic medical factors. Intrinsic medical factors were more common in males than in females. Drivers with intrinsic medical factors were often at fault and usually crossed over to the wrong side of the road and crashed into an oncoming vehicle or roadside object. In 6% of the drivers, intrinsic medical factors were probably the underlying cause of the crash; in 1.3% the probability was strong. In the ≥60-year-old group, intrinsic medical factors were the underlying cause of the crash in 19% of the cases; the probability was strong in 4%.
