Nineteen percent of 9 years old Irish children are overweight; seven percent are obese. Our aims were: to examine whether differences exist between paternal self-reported and measured height, weight and BMI in a population representative sample; and to explore paternal perceptions of their own weight status. Measures of height and weight for fathers and for their children from the National Longitudinal Study of Children Growing Up in Ireland were obtained using validated methods. Three quarters of fathers (6,263 of 8,568 study children) with a mean age of 42 years (SD 5.04) responded. The mean difference between self-reported and measured weight was -1.03kg (SD=4.52), indicating that weight was underestimated. Obese fathers were more likely to have an obese son (9.4% compared to 5.3% for the full cohort) and an obese daughter (12.4% compared to 7.7%). These data suggest that there is a strong relationship between fathers' weights and his childrens’ weights. A leading factor in the development of childhood obesity is parental obesity. Targeting overweight and obesity in the child should occur simultaneously with tackling overweight and obesity in the parents; in this study, the fathers.