This paper reports an intensive follow-up study of persons injured while wearing seat belts in crashes. Examinations of both vehicles and persons were carried out after the crash, and 30 out of 54 (55.5%) persons were judged to have been wearing seat belts at impact. Eight received injuries from the seat belt, only four of these injuries being severe, and none was fatal. A roadside survey showed that half of the occupants wearing seat belts had them adjusted incorrectly. This compared with nearly 90% of the crash cases having incorrectly adjusted belts. There is therefore an association between incorrectly worn seat belts and injury. The seat belt buckle seems to be a possible cause of injury in this situation, especially when worn in from of the hip, and with a loose belt. Comparison of police reports of belt wearing for the study cases suggests an underestimate of about 10% in the wearing rate if police data are used.