Osteoid osteoma is a small, oval or roundish, nidus like neoplasm of bone. The lesion usually does not exceed a centimenter in its greatest dimension, and it consists of osteoid, trabeculae of newly formed osseous tissues and a substratum of highly vascularized osteogenic connective tissue. In a differential diagnosis, consideration should be given to Brodies abscess, sclerosing osteomyelitis of Garre, Fibrous dysplasia and healing fractures. From Janua 1960 to December 1980, we have seen and studied 18 cases of osteoid osteoma and the results obtained from this study were follows: l. Eleven cases were found in second decade and 17 cases were developed before thirty years old. 2. The sex ratio was nearly equal and duration of disease from onset was average 16 months. 3. Location of lesions were predominantly in lower extremities, 9 in tibia and 3 in femur. 4. Pain was noted in 16 cases and aspirin affected in 8 cases. 5. Nidus was found in 11 cases. 6. All cases were treated by radical excision of lesions with disappearance of pain and satisfactory results.