The main object of this historical follow-up study in a dynamic population was to examine the extent of fatal unintentional child injuries in Denmark. Particular attention was paid to identifying risks and risk groups as targets for prophylactic measures. All 1,202 fatal injuries which occurred during 1976-85 and were reported to the police were included in the study. Death certificate information was supplemented by data from medical files, post-mortem medical examinations and police reports. The average mortality rate (MR) was 14.43 per 100,000 person-years in the group of boys, and 8.21 per 100,000 person years among girls. The cumulative mortality proportion was 2.18 per thousand for boys and 1.25 per thousand for girls. The mortality for boys fell during the period, but remained constant for girls. In the last years of the study the mortality rate for both sexes approached the same level. Boys had an overall mortality rate twice that of girls (RR 1.75 (CI 1.56-1.97)). Mortality was highest in the first five years of children's lives, i.e. the period of motor development and increasing curiosity regarding their surroundings. An overmortality in the rural areas as compared with the urban areas was identified (RR 1.47 (CI 1.31-1.64)). One reason for this may be that children Living in rural areas are exposed to greater risks in everyday life and that they must venture into the traffic for purposes of social contact. Traffic-related deaths comprised 58% of all unintentional injury deaths. In around 50% of all cases the cause of death was head injury. The most common external cause of death were pedestrian injuries (20.7%), bicycle injuries (20.5%), occupant injuries (12.8%), drownings (12.2%) and suffocations/aspirations (11.1%). The relative distribution of the external causes of injuries varied according to age and sex, which indicates that the risks to which children are exposed depend upon their age, and that any parental guidance must accord with the risk to be avoided and the age of the child. It is concluded, that fatal child injuries are a serious health problem. Profylactic efforts should be directed towards children in the younger age range living in rural areas. The vast majority of deaths are caused by traffic injuries. Special priority should be attached to pedestrian and bicycle injuries together with drownings.