Although mortality and incidence rates of pyogenic osteomyelitis and arthritis have been reduced significantly due to development of treatment methods and antibiotics, the resistance of bacterias to antibiotics, especially in gram negative infections which increase rapidly in recent years, posess many difficult problems in the treatment of bone and joint infections. We have analysed 124 patients of gram negative bone and joint infection admitted in Seoul National University Hospital from Jan. 1976 to Dec. 1985. The following results and conclusion were drawn; 1. The ratio of gram negative infections to total pyogenic infections was 39.2% and has been increased annually. 1. The incidence of gram negative infections under 20 years of age was 54.0%, and male was 1.7 times as much affected as female. 3. Involved sites of pyogenic osteomyelitis were femur(32.6%), tibia(25.6%), humerus(6.2%), and those of pyogenic arthritis were hip(12.4%), knee(7.0%), shoulder(2.3%), and ankle(2.3%). 4. Original diseases of gram negative infection were hematogenous osteomyelitis(41.1%), infected nonunion(33.1%), pyogenic osteomyelitis(16.9%), sepsis(4.8%), and infected total hip replacement arthroplasty(4.0%). 5. Incidence rate of gram negative infection, especially mixed gram negative infection rather than pure gram negative infection, was increased annually. 6. Sensitive antibiotics for gram negative organisms were turned out aminoglycosides such as Amikacin and Tobramycin in general, however, the, resistance to that antibiotics increased annually. 7. In the view that resistance rate of gram negative organisms to antibiotics increased annually, it cannot be too much emphasized that the most sensitive antibiotics to be used must be chosen according to the results of antibiotics sensitivity test, and that further advanced effective antibiotics should be developed.