Pyogenic osteomyelitis is a frequent and difficult disease in treatment in orthopedic surgery. The various manifestation of the disease related to the causative organisms, the sites of involvement, the pathogenesis and the clinical course tend to give a bad prognosis after treatment. This study consists of three hundred and twenty four cases of pyogenic osteomyelitis which are studied at the Department of Orthopedic Surgery, Yonsei University hospital for 7 years and 8 months from January 1973 to August 1979. The results are as follows: 1. The frequency of the disease was highest in 1977 but not significant. 2. Femur and tibia were most frequently involved. (65.4%). 3. Age distribution showed the highest incidence between 6 and 15 years of age. (60.6%) Sex ratio was 2(M):1(F) 4. The causative organism was mostly Staphylococcus. (80.5%) The coagulase(+) Staphylococcus showed the highest sensitivity to cefamezine (88.8%) and the highest resistance to penicillin. (89.7%) 5. The treatment had been carried out case by case with variable methods. Author considered the best method of treatment was early decompression and massive antibiotic therapy in acute osteomyelitis, and saucerization with closed irrigation system in chronic osteomyelitis.