Forty five cases of osteoid osteoma operated at the Department of Orthopedic Surgery, Seoul National University Hospital from Jan. 1962 to Oct. 1990 were analyzed with review of the literature. Most patients (73.3%) were in the age of 10-25, and male-female ratio was 1.37:1. Femur (47.8%) and tibia (34.8%) were the most frequent site of the lesion. Pain was the most frequent chief complaint (81.2%), and the remaining patients complained of palpable mass, limping and muscle atrophy. Two cases of painless osteoid osteoma were identified, at a middle phalanx and a tibial diaphysis, respectively. Simple roentgenography, simple tomogram, bone scanning, computerized tomography and magnetic resonance imaging were the tools used for diagnosis and localization. Nidus was identified at postoperative histopathologic examination in 40.6% of the cases. Excision was the preferred method of treatment and curettage including nidus was done for the remainders. Four cases recurred, including a case where nidus was identified at histopathologic examination after the first operation.