According to data from the emergency room of the Odense University Hospital the number of bicyclists treated following road traffic accidents with a counterpart has increased 90% from 1980 to 1990 In the same period there has been little increase in the intensity of the bicyclist’s traffic while motor vehicle traffic intensity has increased.

The objective of this study was to reveal factors in the development of the bicycle accidents which might explain the increase in bicycle collision accidents. Furthermore we wanted to examine if the official road traffic accidents statistics gave a true picture of the accident development compared to data from the emergency room.

During a number of years the data from all persons treated in the emergency room has been collected by the Accident Analysis Group at the Odense University Hospital and stored in a database. These data are compared with data from the police records from the National Bureau of Statistics.

The largest part of the increase in bicyclist’s collision accidents is caused by a higher number of collisions with other bicyclists and motor vehicles. The number of collisions with pedestrians, mopeds and motorcycles is relatively constant. The bicyclists age 20 to 29 years cause the largest part of the increase in the number of accidents. The male/female ratio is almost constant. The severity of the lesions decreases significantly, whereas the localization of the injuries according to body regions do not change. The decrease in severity of the lesions is accompanied by a smaller rate of hospitalization.

There is a decrease in the rate of police reporting, also if the accidents with minor injuries according to AIS are excluded.