Osteoid osteoma, a frequent lesions of bone, is usually intraosseous but occasionallysubperiosteal. We describe the case of a 19-year-old male with knee pain causedby subperiosteal osteoid osteoma. Radiologic evaluation was performed withradiographic, computed tomography (CT), ultrasonographic (US) and magneticresonance imaging (MRI). But the preoperative diagnosis of osteoid osteoma wasdelayed because of unusual imaging findings and atypical symptom. After excisionalbiopsy, histological examination confirmed the diagnosis of osteoid osteoma. Thelesion was treated successfully with CT-guided radiofrequency ablation.