OBJECTIVE: The purpose of this study was to analyse clinical manifestations and laboratory findings in childhood patients with polyarticularonset juvenile rheumatoid arthritis (JRA). METHODS: Eleven cases of polyarticular JRA who were diagnosed and treated in the Department of Pediatrics, Seoul National University Children's Hospital from June 1988 to May 1995 were investigated for clinical manifestations and laboratory findings. RESULTS: 1) There were 6 males and 5 females and their ages of onset were 4 years to 15.1 years(mean 10.9 years). 2) Systemic manifestations were not observed, but low-grade fever was noted in 5 patients. 3) The involvement of joints was symmetric in 9 patients and asymmetric in 2 patients. 4) The most commonly affected joints were knees and ankles, followed by proximal interphalangeal joints of hand, shoulder, elbow, temporomandibular joint, and other joints. 5) Roentgenographic changes of joints were detected in 6 patients and bone scan in 7 patients showed increased uptake in the involved joints. 6) The main laboratory findings observed were microcytic and hypochromic anemia (64%), thrombocytosis (82%), elevated eryhtrocyte sedimentation rate (100%), positive or increased C-reactive protein(100%), positive rheumatoid factor(RF) (18%), positive antinuclear antibody(ANA) (27%). RF was positive in 2 girls with later age of onset and the pattern of immunofluorescent ANA were all homogeneous. 7) Nonsteroid antiinflammatory drugs (NSAIDs) were used most frequently and steroid with or without sulfasalazine was tried in 4 patients unresponsive to NSAIDs. 8) At last follow-up, 6 cases(55%) were classified as functional class I, 4 cases(36%) as class II, and 1 case(9%) as class III. CONCLUSION: These data showed the clinical manifestations and laboratory findings of polyarticularonset juvenile rheumatoid arthritis in Korean children.