Abstract: Objective: To reduce the misdiagnosis rate of osteoid osteoma by analyzing its symptoms,signs,and X-ray findings. Methods: Nine cases of osteoid osteoma（7 males and 2 females） confirmed by histopathology were chosen.All patients underwent plain X-ray examination and CT scanning,and one of them had MRI. Results: All cases had persistent night pain in the hip joints,which caused symptoms of limp and muscular atrophy in the affected leg.The osteoid osteoma was found to have a circular or oval radiolucency（nidus） which was less than 2 cm in diameter with different degrees of bone sclerosis around the nidus.Of the 9 cases,5 showed an irregular area with less density on plain X-ray film.CT scanning showed nidus in all cases.MRI showed nidus in 1 case.Radioactive scanning showed radioactive concentration in 4 cases. Conclusion: Pain is the main symptom and nidus is the key to the diagnosis of osteoid osteoma.CT scan is the best method to demonstrate the nidus.The reason why osteoid osteoma is misdiagnosed is lack of knowledge about the disease.