The patient was a 10-month-old male infant. He presented slightly depressed erythematous hard plaques on the left upper chest and left thigh. We had taken biopsies from both skin lesions, confirming cutaneous ossification or bone formation. He also had the characteristic features of AHO. He had a history of admission due to patent ductus arteriosus and atrial septal defect. The laboratory results showed slightly decreased calcium, increased phosphorus and PTH levels. The patient received no specific corrective measures because his calcium and phosphorus levels were not far from normal values until newly developed similar skin lesions appeared.