Functioning and coping of 43 families with children with phenylketonuria (PKU) was investigated. A significant positive correlation was found among perceived family cohesion, dietary adherence associated with metabolic control, and child IQ. Parental education also significantly related to dietary adherence and to higher IQ level in the child. In addition, paternal perception of family adaptability was related to the child's IQ. Child depression as perceived by the parents was related to family functioning and coping variables. Functioning of PKU families is discussed in relation to current theories of family functioning under stress.