After the discovery of penicillin by Fleming, a great improvement in the treatment of osteomyelitis was obtained and the mortality rate in the acute stage was markedly decreased. But, because of abuse of the antibiotics and resulting resistant organisms to antibiotics, the incidence of acute hematogenous osteomyelitis tends to increase recently. During the period of 6 years extending from 1979 to 1984, we have treated 45 cases of acute hematogenous osteomyelitis in children and clinical analysis was made about the causes of the development of chronic osteomyelitis with particular emphasis on the time interval from onset to treatment, and on the operative methods in the surgical treatments. The following results were obtained; 1. The incidence in males was 1.5 times greater than females. 2. Age incidence showed that it was most prevalent in the age group of 6 to 15 with 66.2% of the total cases. 3. The most common sites of the involvement was femur and tibia in orders. 4. Most of cases showed pain, local tenderness, pyrexia, loss of motion, swelling, and heat of the involved limbs. 5. Among the causative organisms, staphylococcus aureus was most prevalent one. 6. Cephalosporin, methicillin, gentamicin showed the highest sensitivity while penicillin showed marked resistancy (80%). 7. Time interval from onset to treatment was persistently an important factor in the development of chronicity. 8. Bone fenestration was the best method in the surgical treatments of acute hematogenous osteomyelitis in children. 9. Early diagnosis, adequate antibiotics, and early surgical decompression and drainage (esp. bone fenestration) were considered to be the essential part of management of acute hematogenous osteomyelitis in preventing its chronicity.