Objective To evaluate the clinical and imaging characteristics of osteoid osteoma in femoral neck and to improve diagnostic accuracy of this disease.Methods Twenty-one patients (18 males and 3 females,age,7-26 years,median age,13 years) with pathologically proven osteoid osteoma of the femoral neck were retrospectively analyzed for their clinical profile and radiologic features.CT and X-ray examinations were performed in all patients,10 of them pefformed post-contrast CT scan and 4 of them performed MRI examinations.Results Nineteen patients had hip pain (pain worse at night in 11,and 8 received salicylates treatment with good response),and 2 patients only with intermittent claudication.The duration ranged from 2 months to 54 months (median duration 12 months).X-ray: Nidus was seen on plain film in 10 cases,18 cases showed different degrees of bone sclerosis of the nidus.CT: Nidus was demonstrated in all cases.Among them,8 were intracortical,6 were subperiosteal,7 were endosteal.Twenty cases showed different degrees of bone sclerosis of the nidus-extra-articular anteromedial cortical surface of the femur neck.Nineteen cases showed vascular groove sign.MRI: Nidus was seen in 4 cases.Bone sclerosis was low signal on all sequences.Three cases had joint effusion,4 cases had bone marrow edema,and 2 cases had synovial thickening.Conclusions Although osteoid osteoma of femoral neck has non-specific clinical features,the radiographic findings are usually typical.The nidus of osteoid osteoma is often located within the joint.Bony sclerosis occurs at the area of extra-articular anteromedial cortical surface of the femur neck.CT examination remains an optimal method to identify the nidus.