2.295 injured front seat occupants registered at the Odense University Hospital during a 4-year period have been the subject of a closer analysis in order to define possible reasons for the lacking effect of the belt mandatory introduced in 1976. Particular attention was paid to differences of the behavioral pattern of seat belt users and non-users by means of age, hour and type of accident and errand. Several possible factors are discussed which might counteract the predicted effect of the seat belt legislation.