Background and aims The restriction in dietary management of phenylketonuria (PKU) can lead to essential element’s deficiency, anaemia and failure to thrive. The aim of our retrospectiv study was to determine the incidence of iron deficiency in children undergoing specific nutritional therapy for PKU. Methods: The studied lot was formed by 15 children diagnosed with PKU in the Regional Centre for the diagnosis and treatment of PKU from Iasi-Romania and who were at least 12 months under dietetic treatment. Nutritional status, nutrient intake and the laboratory tests (haemoglobin, hematocrit, MCV, MCH, MCHC, red blood cells count, iron, reticulocytes) were assessed at baseline and every 3 months. We also made correllation with the nutritional status of the patients. The patients diagnosed with iron deficiency anaemia were treated with iron 5 mg/kg/day for 3 months. Results: The clinical exam showed presence of palor in 7 cases, anorexia in 6 cases, irritability in 4 cases. Anaemia was confirmed in 10 PKU patients. Haematological parameters correlated with nutritional status revealed more severe anaemia in patients with malnutrition or obesity. After 3 months of treatment, the haematologic parameters normalised in 9 cases. Conclusions: We suggest that the clinical management of patients with PKU include routine evaluation of iron status indices. Prevention or early treatment of iron deficiency may improve cognitive development and behaviour of children with PKU.