Parents of children with phenylketonuria completed behavior rating forms for their affected children who were 8 through 12 years old. The 18 completed forms represented 824570360f the 22 children in this age range followed through one phenylketonuria clinic. The children who had received dietary management discontinued nutrient restrictions at about six years of age. In contrast to a comparison group used to standardize the rating scale, study children on average received ratings higher in distractibility, lower in intensity, lower in persistence, and lower in predictability of behavior. Ratings for activity, adaptability, approach mood and threshold of response were not significantly different between the groups. Within the study group none of the ratings correlated to a significant degree with measures of intelligence, age at diet initiation or age at diet termination.