Background:Osteogenesis imperfecta (OI) is a genetic disorder of connective tissue primarily affecting bone with a wide spectrum of clinical expression that varies from death in the perinatal period to normal life expectancy. Although data is scarce, we observed a high frequency of anemia in patients with OI and hypothesized that functional iron deficiency (FID) may occur secondary to the inflammation resulting from frequent fractures and multiple surgical procedures.Aims:The aim of this work was to study the frequency of anemia in children with OI and try to classify them according to iron status by conventional tests to analyze the possibility of presence of FID and the possible association of hepcidin level with such etiology.Methods:A cross‐sectional study included 56 patients diagnosed with osteogenesis imperfecta regularly following at the genetics clinic, Children'sHospital, Ain‐Shams university. All patients were subjected to detailed clinical scoring with complete blood count, serum iron, serum ferritin, and total iron binding capacity, C‐reactive protein (CRP) and serum hepcidin by ELISA, Dexa scan and lateral and AP spine x‐ray. Patients were classified into five groups, Group‐1 including 7 OI patients fulfilling criteria of FID; serum ferritin > 100ng/ml, TS < 20% and CRP> 1 mg/dl, Group‐2 including 27 OI patients fulfilling criteria of combined ACD&IDA; serum ferritin level was ≤ 100ng /ml, TS < 20% and CRP> 1 mg/dl, Group‐3 including 16 OI patients without anemia according to WHO classification, other anemia group including 6 OI patients with anemia that could not be classified according to the classification adopted in this study, IDA anemia including zero OI patients as there were no patients fulfilling criteria of pure IDA; ferritin < 12ng/ml in children aged <5 years, or ferritin <15ng/ml in children aged > 5 years, when the corresponding CRP was <1 mg/dl and TS < 20%.Results:The frequency of anemia among the studied patients with osteogenesis imperfecta was 71.4%. Combined IDA and FID formed 48.2%, 12.5%, 28.6% and 10.7% hadFID, no anemia and other anemia groups respectively. functional iron deficiency was found in 60.7%.Median hepcidin level was significantly increased in pure FID patients 120 (100 – 510 ng/mL) as compared to those in no anemia patients 80 (65 – 100 ng/mL) and other anemias 60 (50 – 70 ng/mL). The serum hepcidin concentration was mildly reduced in ACD patients with ID with a median of 100 (60 – 150 ng/mL).Patients with severity score levels less than 70% had significant higher number of WBCS, platelets and serum hepcidin levels and significant lower serum iron compared to patients with severity score levels more than 70% and less than 90%.Summary/Conclusion:Anemia is an unrecognized complication in patients with OI. Functional iron deficiency constitutes a significant etiology adding to dietetic problems. New therapeutic approach for FID is suggested to improve the quality of fracture healing in such group.