Philosophiae Doctor - PhD / Injuries, and head injuries in particular, are a common cause of childhood, adolescent and young adulthood morbidity and mortality. The risk factors for injuries in general have been well researched. But it remains uncertain whether these factors are similar for specific injuries, such as head injuries. The inter-relationships between individual and environmental risk factors are difficult to study. Whilst much is know of the short-term consequences of head injuries, relatively little information is available on their long-term conseque~ces. The follow-up period in most research is short (often less than 1 year) and studies are weak in terms of design. Studies generally find a variety of social, cognitive and psychological consequences in children and young adults experiencing head injuries. This study assessed in two large, nationally representative samples, a 1946 birth cohort and a 1997 cross-sectional health survey: 1) the occurrence and risk factors for childhood, adolescent and early adulthood head and other injuries, and 2) the long-term cognitive and psychiatric effects of skull injuries. The overall findings for the risk factors across the two data sets and over 5 decades of data collection were strikingly similar. Maleness was a major risk factor for the head and other injuries. Some of the behaviour and personality factors such as hyperactivity and being neurotic, even after adjusting for sex, socioeconomic status and family type, remained significantly related to injuries, particularly those affecting the head region. A clustering of demographic, socioeconomic, family and behavioural risk factors significantly increased the likelihood of injuries, particularly recurring injuries with at least one being a head injury. In the unadjusted analyses socioeconomic status and family type were less consistently related to injuries. The long-term psychiatric and cognitive consequences of skull injuries causing concussion and skull fractures in childhood and early adulthood were negligible. Other childhood factors such as educational ability, behaviour and personality, and level of education achieved were more predictive of psychiatric symptoms and cognitive problems in adulthood. This study suggests that children and adolescents with behavioural and personality problems were at greater risk of head and other injuries in childhood, adolescence and later in adulthood. Children and adolescents with behavioural and personality problems were more likely to live in manual social class families and families with a single parent or stepparent. This combination of behavioural problems and deprived socioeconomic and family circumstances may increase tendencies for violent behaviour, alcohol dependence and manual occupations later in adulthood, which all increase the risk of injuries. There is therefore a need to identify children and adolescents with behavioural and personality problems as early as possible to prevent the impact in the short- and longterm. This will not only reduce the burden of injuries but also the many other consequence of behavioural and personality problems, particularly when located within deprived socioeconomic and family circumstances.