Subacute osteomylitis is far less common than acute osteomyelitis, characterized by insidious onset of the symptoms of mild local pain or discomfort without any acute systemic illness. Radiographic findings are not infrequently confused with benign or malignant bone tumors. From Jan, 1983 to Dec. 1991, we experienced twelve patients with subacute osteomylitis of long bones. Our clinical observations were as follows. 1. There were 11 boys and one girl with an average age of 9.7 years(range, 30months-16years). 2. The involved sites were proximal in 1, distal radius in 3, midshaft of femur in 3, distal femur in 2, proximal tibia in 1, and distal tibia in 2 cases. 3. All patients had insidious onset of mild to moderate pain. ESR was increased in 9 cases(75%) with a mean value of 44 mm/hr, but leukocytosis was not found. 4. According to the Green and Edwards' classification, there were type 1 in 1, type 2 in 3, type 3 in 3, and type 6 in 5 cases. 5. Eleven patients had operative treatment. The remaining one patient was treated by antibiotic treatment. 6. Primary treatment was successful in 11 patients who were followed for and average 9.5 months. One patients was lost to follow-up.