This booklet summarizes current knowledge about phenylketonuria (PKU), an inherited condition that results in severe mental retardation if untreated, and discusses the psychoeducational implications of the condition. The introduction stresses the importance of early diagnosis (during the first days of life) and the effectiveness of a diet that avoids the amino acid phenylalanine in preventing mental retardation. Individual sections summarize information about screening, diagnosis, and incidence; diet management; the role of school personnel; the elementary student with PKU; and the adolescent student with PKU. The booklet outlines four major responsibilities of teachers, counselors, administrators, and staff when a PKU child enrolls in their school: (1) treatment of the child as a normal, healthy student; (2) establishment and maintenance of open communication with the student and parents in order to facilitate good dietary management; (3) encouraging the adolescent student to continue the restricted diet; and (4) identification of students with possible PKU who are not on the special diet. A glossary defines key terms. A list of resources includes clinics for treatment, materials for parents of young children with PKU, booklets and videos explaining PKU to children and youth, materials concerning maternal PKU, references for teachers and other professionals, and references in the medical literature. (Contains 25 references.) (DB)