Background: Phenylketonuria is an autosomal-recessive inborn error of amino acid metabolism characterized by elevated blood phenylalanine. The study aimed to: assess adjustment patterns of children suffering from phenylketonuria. Setting: This study was conducted at genetic clinic in outpatient department belonging to Children's Hospital affiliated to Ain Shams University Hospitals. Design: Descriptive research design was utilized. Sample: A purposive sample of 60 children attending with their mothers in the previously mentioned setting over a period of 6 months and were satisfying the inclusive criteria. Tools: Three tools were utilized in this study. The first tool was a structured questionnaire sheet to assess children' knowledge regarding phenylketonuria, the second tool was psychometric assessment to assess psychological problems of children with phenylketonuria, the third tool was Adjustment patterns scale of children with phenylketonuria. Results: The study findings revealed that three quarters of the studied children had unsatisfactory knowledge regarding phenylketonuria. Also, half of the studied children had severe level of anxiety and more than two thirds of them had low self-esteem. There was an extremely statistical significant difference and positive correlation between children's total knowledge and total adjustment patterns. Conclusion: the minority of the studied children always adjusted with their disease. There was statistical significant difference between the studied children's characteristics and their total level of adjustment patterns. Recommendations: Continuous health educational programs about adjustment patterns should be provided for children suffering from phenylketonuria to cope positively with their disease.