Background: The goal of this study was to assess the anthropometric and biochemical parameters of children and adolescents with phenylketonuria (PKU).Methods: The participants in this cross-sectional study ranged in age from 4 to 18. Biochemical markers such as blood vitamin B12, folic acid, iron, ferritin, calcium, 25-hydroxy vitamin D3, zinc, and plasma phenylalanine (phe) and tyrosine (Tyr) levels were evaluated, as well as demographics and anthropometric measurements. A 3-day dietary recall questionnaire was completed by all individuals.Results: Eighty percent (64) of the 80 patients (42 females, 52.5%) had typical PKU. Consanguineous marriages were found in 57.5% (46) of the patients' parents. According to the height for age index, 17.5% of the study group (n = 14) were short or very short. According to age-related weight and body mass index (BMI) indices, 37.5% (n = 30) and 43.8% (n = 35) of people are obese or overweight, respectively. Biochemical testing revealed raised vitamin B12 levels and 25-hydroxy vitamin D3 deficiency in 28 (35%) of the patients, insufficient folic acid in 10 (12.5%), and elevated phenylalanine levels in children under 12 years old 45 (70.3%) and adolescents 10 (62.5%). A high phe intake (OR = 4.44, CI %95 = 1.27-15.57) is one risk factor for obesity and overweight.Conclusion: Patients with phenylketonuria had a high rate of overweight and obesity, according to anthropometric measurements. PKU patients who are overweight or obese do not differ from normal-weight patients in terms of dietary intake or laboratory findings (except for serum iron levels).