Behavioural feeding problems were found to be more prevalent in a group of 15 PKU children aged 1-5 years when compared to non-PKU controls. The parents of PKU children identified poorer appetites (p < 0.01), a more limited range of foods consumed (p < 0.03) and more gastrointestinal symptoms such as vomiting and constipation (p < 0.03) than control children. The children were slower to feed (p < 0.03), were more likely to dislike sweet foods and some ate separately from the rest of the family at mealtime (p < 0.03). The effects on normal feeding behaviour should be considered when advocating strict diet therapy for young PKU children.