The association of social and family factors with triceps skinfold and weight for height and age was assessed using multiple regression analyses for 5-11 year-old-children in England and Scotland. Parents' body build was the factor most consistently associated with the two proxy measures of obesity. Number of siblings in the family was inversely related to triceps skinfold thickness. Parents' body-build and number of siblings were more strongly related to our measures of obesity in the older age groups and in girls, whereas child's birth-weight was more associated with weight for height and triceps skinfold in the younger age groups. Father's social class and mother's education made almost no contribution to the variation of triceps skinfold and weight for height in children. The relative risk of obesity associated with any individual independent variables was less than or around two. We conclude that there is little scope for identifying the majority of children at risk of obesity in a characteristic social environment. However, the increase in the association between our measures of obesity in parents and older children provides a possible tool for the early detection of children who may become obese.