Sixty-seven cases of osteoid osteoma were studied at the Hospital for Joint Diseases between 1980 and 1989. The lesions were categorized according to location: medullary, cortical, or subperiosteal and were further grouped as intracapsular and extracapsular. The histologic features of trabecular thickness, reactive bone formation, proportion of fibrovascular stroma, and ratio of osteoid and mineralized matrix were examined. The radiographic features were compared. The literature is reviewed. We include our experience with tetracycline labelling.