Acute pyogenic osteomyelitis is frequent in infants and children, usually hematogenous, and predominant in male. The etiology of acute osteomyelitis is of 3 types: hematogenous, direct innoculation, or postoperative. Acute pyogenic hematogenous osteomyelitis is the most frequent type in children. This study consisted of 119 cases of acute pyogenic osteomyelitis which were studied at the department of orthopedic surgery, Yonsei university, Severance hospital and Youngdong hospital for 10 years from Jan. 1974 to Dec. 1983. The result were as follows. 1. There were tendency to decrease the frequency of this disease graduaUy since 1973 except 1978. 2. 20 patient (16.8%) had the history of trauma and 43 patients (36.1%) had the entry site of infecting organism. 3. The most frequent involved sites were femur and tibia. 4. E.S.R. was definitely increased in 90.4% of male, in 100% of female. 5. 59.6% of patients revealed the definite bone change at admission on X-ray findings. 6. Staphylococcus coagulase positive was the most frequent organism isolated (95%). 7. The most sensitive antibiotics was cephalosporin and the most resistant was penicillin (90.2%). 8. The antibiotics treatment with immobilization of involved site was initially tried, if there was no symptomatic improvement, the various surgical process was performed with satisfactory result.