This study evaluated adherence to current dietary recommendations of children with cystic fibrosis and mild lung disease and their siblings by comparing energy intake. Fifty children (25 with cystic fibrosis) aged between 7 and 12 years completed the study. Energy intake was assessed by weighed dietary intake, resting energy expenditure was used to calculate recommended daily intakes. The children with cystic fibrosis had significant deficits in Z scores for both height and weight compared with their siblings, but there was no difference in percentage of ideal weight for height. The cystic fibrosis group had a significantly higher energy intake per kilogram body weight per day but there was no difference in the percentage of energy derived from fat, protein or carbohydrate. Energy intake (per kg/day) and fat intake (g/kg) were both significant predictors of weight for height in the cystic fibrosis group. Targets for dietary management in cystic fibrosis should perhaps be related to fat intake per kilogram body weight.