Pyogenic arthritis remain a difficult problem, despite the availability of a wide range of powerful modern antibiotics. Early and correct diagnosis is imperative to assure the prompt initiation of an effective therapeutic regimen and the prevent of late sequela. Careful clinical, laboratory and roentgenological analysis are fundamental to early and precise diagnosis. Therefore, plain roentgenogram should not be overlooked. A radiological and clinical observation was made in 51 cases of pyogenic arthritis admitted to Chosun University Hospital during the period from January 1976 to December 1983 and following results were obtained. 1. Among the 51 cases, 36 cases (70.6%) were male and 15 cases (29.4%) were femals. The most prevalent age was 5 to 9 (27.6%) 2. Symptom duration less than 5 days was in 21 cases (41.2%) and more than 31 days was in 6 cases (11.7%). 3. The most common symptom on admission was pain around the involved joint and others are limitation of motion, swelling, tenderness, fever, local heating and erythema. 4. The underlying causes were composed of unknown in 21 cases (41.2%), trauma in 18 cases (35.3%) infections focus in 8 cases (15.7%) and iatrogenic reason 4 cases (7.8%) 5. The most commonly affected joint was hip joint (45.1%) The other affected sites in order of frequency were knee, ankle, shoulder, S-1 and elbow joint. In infants and children, hip and knee joint are commonly affected: in adults, knee joint is most commonly affected. 6. In laboratory findings, the number of W.B.C and E.S.R were increased in 56.9% Symptom duration more than 31 days in 5 cases were increased E.S.R only. Causative microorganism was isolated in 31 cases : the most common microorganism was Staphylococcus aureus in 22 cases. Others are B-hemolytic Streptococcus, Enterobacteriaceae species and Pseudomonas aeruginosa. 7. In 26 cases (50.9%) of the patients, roentgenographic finding was negative. The most common radiological finding was soft tissue swelling and the others are include in order of frequency: joint space widening, small erosions in articular cortex, subchondral osteoporosis. The common radiological findings of symptom duration more than 31 days in 6 cases were lost of entire cortex, ankylosis and joint space narrowing.