Age, sex, type of fracture and the circumstances causing the injury were studied in altogether 8,682 fractures in children, aged 0 - 16, which had occurred 1950, 1955, 1960, 1965, 1970 and 1975 - 1979. For studies of incidence, the years 1975 - 1979 were chosen and for secular trend studies 1950, 1955, 1960, 1965, 1970 and 1975 - 1979. The following conclusions may be drawn: 1. The risk of fracture increased with age up to age 11 - 12 in girls and 13 - 14 in boys. 2. The accumulated risk of fracture was 27 per cent in girls and 42 per cent in boys. 3. Fractures were more common in boys of all age groups. 4. Over the last three decades the risk of fracture was doubled in boys as well as in girls. 5. Over the years more and more fractures were caused by slight trauma whereas the more severe trauma - even if increasing somewhat in risk - contributed a smaller fraction of the injuries. 6. For the various types of fracture the pattern of change could differ - some increased in incidence, whereas some remained unchanged or even decreased. 7. All types of trauma - horse riding accidents excluded - were more frequent in boys. 8. The most commonly fractured region was the distal end of the forearm followed by the phalanges of the hand and the bones of the carpal-metacarpal region. 9. Playing, sports and traffic, in that order contributed 24, 21 and 12 per cent of those fractures in which the circumstances of the accident could be analysed. 10. Traffic accidents increased with one third in boys as well as in girls. 11. The passive participants in traffic - pedestrians and passengers in motor vehicles - were not more frequently injured during the latter part of the period under observation - a tendency of increase in girls was compensated for by a decrease in boys. 12. Sports and various playing activities as a cause of fracture increased with a factor of five. 13. In the upper limb, the left side was most frequently fractured. 14. The occurrence of fractures varied with the seasons with peak values in May and August and low values in July and December. 15. No fracture type in children could completely meet the criteria of a fragility fracture such as seen in old age. 16. Sustaining one fracture carried an increased risk of an additional fracture especially in the very young children. 17. Fractures not requiring reduction increased the most over the years. 18. The subset of children with various diseases suspected to interfere with skeletal development carried an increased risk of fracture. 19. Some age-related fracture patterns could be traced but they were not very distinct.