Most studies, which are retrospective, show contradictory results regarding the incidence of road traffic accident among diabetic patients. The most frequent cause of accident is hypoglycemia. One should also consider impaired vision (retinopathy, maculopathy), neuropathy (feet insensitivity) and sleep apnoea in overweight patients. Hypoglycemia not only leads to impaired judgement during driving, but also to a reduction in performances, frequent hypoglycemias impair symptom recognition and increase the risk of loss of consciousness. Patients should benefit from teaching about hypoglycemia, i.e. how to recognize and correct it in order to avoid accidents. Generally they should not drive if their glycemia is under 5 mmol/l without correcting it with an adequate amount of carbohydrates.