The decision to continue treatment for phenylketonuria (PKU) patients into adolescence and adulthood presents a challenge to nutritionists and other professionals who must motivate patients to maintain the diet and give them support. Nutrition needs must be assessed and then met by commercial low-phenylalanine formula and low-protein foods, while at the same time the amount of phenylalanine in the diet is severely limited. Combinations of products can be used to tailor the diet to individual needs, e.g., weight reduction. The objective is to allow the intellectually normal PKU patient to develop as socially normal a life-style as possible.