Phenylketonuria (PKU) is an autosomal recessive metabolic genetic disorder characterized by a mutation in the gene for the hepatic enzyme phenylalanine hydroxylase (PAH). The disease may present clinically with seizures, albinism (excessively fair hair and skin), and a ''musty odor'' to the baby's sweat and urine. In the untreated classic case, mental retardation is severe, precluding speech and toilet training. Seizures are common in the more severely retarded, usually start before 18 months of age. This study aimed to identify clinical profile and impacts of newly diagnosed (untreated) PKU on children. Children presented to the Pediatric Department, or Pediatric Neurology Clinic, Sohag University Hospital in whom the diagnosis of Pheylketonuria was established based on measuring phenylalanine level in blood samples were eligible for this study. All studied patients were subjected to thorough history, full examination, and developmental assessment. Electroencephalography (EEG), computed tomography of the brain (CT), phoniatric and audiologic evaluations were also done. During the period of the study we diagnosed 24 cases with phenylketonuria, the main clinical presentations were global developmental delay, hyperactive symptoms, seizures, and autistic features. CT of the brain showed that 58.3% of cases had atrophic changes. EEG showed that 58.3% of cases had abnormal findings as generalized epileptic discharges, focal epileptic discharges, and hypsarrhythmia. We concluded that untreated phenylketonuria still represents a significant burden on children development and mental function in Upper Egypt. So we recommend establishment of national screening programs and pushing it forward as well as immediate development of specific metabolic centers in various universities and research institutes.Ó 2013 Production and hosting by Elsevier B.V. on behalf of Ain Shams University.