Corticosteroids have been widely used in the treatment of idiopathic thrombocytopenic purpura (ITP). We evaluated the late side effects of high-dose methylprednisolone (HDMP) therapy on bone metabolism in children with ITP. Twenty-eight children with acute ITP treated with HDMP (30 mg/kg/d for 3 d then 20 mg/kg/d for 4 d) and 28 controls were enrolled in the study. Bone mineral density (BMD), urinary calcium creatinine ratio, urinary levels of deoxypyridinoline, serum levels of calcium, phosphate, parathyroid hormone, total alkaline phosphatase, and bone-specific alkaline phosphatase were measured in both groups. Magnetic resonance imaging of the femoral head was performed only in study group. The mean levels of serum phosphate, parathyroid hormone, urinary deoxypyridinoline, and calcium creatinine ratio were significantly increased in the study group. There was no significant difference between the 2 groups in terms of serum calcium, total alkaline phosphatase, bone-specific alkaline phosphatase, and BMD values. There was a statistically significant negative correlation between cumulative steroid dose and BMD values in study group (r = -0.379). Osteonecrosis was observed in 3 of 25 patients by magnetic resonance imaging. In conclusion, HDMP therapy, especially in high cumulative doses, increases the bone resorption and may cause osteonecrosis in children with ITP.