The association of various features of family life with obesity in childhood is well established, but less is known about the effect of these influences on the risk of later obesity. In this prospective, population-based study, we examined the influence of parental care in childhood on the risk of obesity in the offspring in young adulthood. In 1974, 1258 pupils aged 9-10 years were randomly selected from the third grade of Copenhagen schools. Information on 987 pupils was obtained from the form teachers on family structure and the perceived support from the parents; school medical services reported on the child's general hygiene. 756 (86%) of the 881 eligible participants were followed up 10 years later. The influence of family factors in childhood on the risk of obesity (body-mass index > 95th centile) in young adulthood was estimated by odds ratios with control for age and body-mass index in 1974, sex, and social background. Family structure (biological or other parents and number of siblings) did not significantly affect the risk of adult obesity. Parental neglect greatly increased the risk in comparison with harmonious support (odds ratio 7.1 [95% CI 2.6-19.3]). Dirty and neglected children had a much greater risk of adult obesity than averagely groomed children (9.8 [3.5-28.2]). However, being an only child, receiving overprotective parental support, or being well-groomed had no effect. Parental neglect during childhood predicts a great risk of obesity in young adulthood, independent of age and body-mass index in childhood, sex, and social background.