Primary subacute pyogenic osteomyelitis is defined as a bone infection of insidious onset lasting for more than several weeks without any acute systemic toxic reactions and is known to have the problem of diagnosis because there is no inflammatory symptoms or signs and X-ray findings are similar to various bone tumors. Authors reviewed 29 cases of primary subacute pyogenic osteomyelitis of long bones admitted at Fatima hospital during the years between 1976 and 1984. The osteomyelitis of infants and the osteomyelitis modified by antibiotics were excluded. The diagnosis of the cases was confirmed by bacteriological examination and/or tissue examination. The results were as follows. 1. The cases were 18 males and 11 females and 19 adults and 10 children. Male predominence was noted in children. 2. The involved bones were 11 tibias, 10 femurs and all other long bones. The involved sites were 18 metaphysis and 11 shafts. 3. All of the cases has insidious onset of local pain without any acute systemic symptoms and most of the cases has local tenderness but local deep swelling noted in about half of the cases. 4. There were many cases with elevated ESR and a few cases of slight leukocytosis. 5. The confirmed infecting organism was all staphylococcus in 16 cases of the cultures from the 25 lesions. 6. The X-ray findings were Brodies abscess in 10, illdefined cavity in 3, diffuse bones absorption in 5, diaphyseal lesion of adult with localized cortical sclerosis in 5 and with localized medullary abscess in 3 and diaphyseal lesion of children with localized medullary abscess and periosteal reaction in 3 cases. 7. All of the cases cured rapidly with rare recurrence after treatment by simple local excision in 4 and curettage in 22 cases combined with antibiotic therapy and local immobilization.