Background: Hemoglobin H (HbH) is usually recognized as mild thalassemia. However, a wide range of clinical manifestations, from fatal hydrops fetalis to asymptomatic mild anemia, is observed. A severity scoring system to guide the management of patients with HbH is needed. Objective: To develop a scoring system to predict the necessity of regular transfusion among patients with HbH. Methods: Patients were classified into 2 groups according to transfusion requirement: severe among transfusion-dependent thalassemia (TDT) and nonsevere among nontransfusion-dependent thalassemia (NTDT). Clinical and hematological parameters associated with transfusion dependency were identified and β-coefficients of significant parameters from multiple logistic regression analysis were used to develop a scoring system. Results: A total of 247 pediatric patients (24 severe, 223 nonsevere) with a median age of 14.3 (IQR 9.9-18.4) years were included. Multiple logistic regression analysis revealed 3 significant parameters associated with regular transfusion requirement including 1) age at diagnosis <2 years, 2) spleen size ≥3 cm and 3) Hb at steady-state <8 g/dL. Coefficients of the respective parameters were used to define the scores as 1, 2 and 2, respectively. A total score of ≥3 was associated with regular transfusion requirement among severe HbH (sensitivity 88%, specificity 83%). The newly developed scoring system was validated in the second cohort of 134 pediatric patients with HbH treated at another center. The cut-off score ≥3 yielded comparable sensitivity and specificity for the prediction.