The adult long bone is known to be very rarely infected by the hematogenous route because of the different vascular pattern from the children and the clinical pattern of the primary hematogenous pyogenic osteomyelitis occurred in adult long bones is very different from the well known acute osteomyelitis of the children. The authors studied 16 cases of the hematogenous pyogenic osteomyelitis occurred in the adult long bones without previous history of the bone infection and the diagnosis was confirmed by histological and/or bacteriological examinations. The cases were 8 males and 8 females having ages between 19 years to 50 years old. The involved bones were 6 femurs, 5 tibias, 2 humeri and fibulas and a ulna and the involved sites were 10 in shafts and 6 in ends of long hones. All the cases had insidious onset without acute symptoms and the course was rather subacute form. There were three different types based on x-ray findings and operative findings. 5 cases were cortical type having localized cortical thickening in the shaft around one or several small intracortical ahscesses, 7 cases were medullary localized type having well circumscribed bone abscess and 4 cases were medullary diffuse type having extensive irregular destruction with occasional small sequestrum. The problems of these cases were differential diagnosis because there were no typical symptoms or signs of the infection and the x-ray findings were very confusing, but most of the cases healed well hy simple surgery and antibiotics.