Inborn errors of metabolism are a group of inherited genetic disorders in which the body is unable to properly metabolize certain nutrients because of the absence or deficiency of specific enzymes. These disorders often result in the accumulation of toxic substances or the deficiency of essential metabolic products. Early diagnosis through newborn screening and appropriate dietary management are essential to prevent severe complications and ensure normal growth and development. Phenylketonuria (PKU) is an inherited metabolic disorder caused by a deficiency of the enzyme phenylalanine hydroxylase, which converts the amino acid phenylalanine into tyrosine. As a result, phenylalanine accumulates in the blood and tissues, causing toxic effects on the brain and nervous system. PKU is inherited in an autosomal recessive pattern. If left untreated, it can lead to intellectual disability, developmental delay, seizures, behavioral problems, eczema, light skin pigmentation, and a characteristic musty odor of urine and sweat. Early diagnosis through newborn screening has significantly improved the prognosis of affected individuals. The dietary management of phenylketonuria focuses on maintaining blood phenylalanine levels within the recommended range while ensuring adequate nutrition for normal growth and development. A low-phenylalanine diet is started immediately after diagnosis and is continued throughout life. High-protein foods such as meat, fish, eggs, milk, cheese, nuts, pulses, and soy products are restricted because they contain large amounts of phenylalanine.