Obesity and overweight are prevalent in children of diabetic mothers. This could be the consequence of the diabetic pregnancy causing macrosomia in the newborn as well as the expression of a thrifty genotype leading to diabetes in the mother and obesity in the child. In an attempt to distinguish between the effects of the prenatal environment, and genetic influences, anthropometric parameters were compared between children of 19 diabetic mothers and 21 diabetic fathers. Age- and height-adjusted weight indices and skinfold ratios were significantly higher in children of diabetic mothers than in children of diabetic fathers. It is concluded that intrauterine environmental factors have a lasting effect on later body build. The additional risk of children of diabetic mothers to become overweight and possibly obese in later life should be prevented by careful control of diabetes during pregnancy.