Objective: To define the prevalence, pattern, and clinical course of arthritis presenting at the time of diagnosis of Kawasaki disease. Study design: A single-center, retrospective study of 414 consecutive patients diagnosed with Kawasaki disease between January 1997 and December 2002 was performed. Standardized clinical assessments, laboratory and imaging test results, and treatment regimens were reviewed. The clinical, laboratory, treatment response,and coronary outcome data were analyzed for children with and without arthritis. Results: The prevalence of arthritis was 7.5%(31/414). In the 31 children with arthritis,55%had oligoarticular involvement and 45%had polyarticular involvement. In both of these groups, the large joints were predominantly involved. Some 88%of the children with arthritis responded to standard intravenous immunoglobulin therapy for acute Kawasaki disease and did not require additional medications. The children with arthritis had significantly increased levels of inflammatory markers, but their demographical and clinical features were otherwise similar to those of the children without arthritis, including coronary outcome, with the same proportion(13%) of children from each group having coronaryartery lesions (z-score ≥2.5). Conclusions: Arthritisis a short-lived phenomenon included in the clinical spectrum of acute Kawasaki disease. Children with arthritis have evidence of increased systemic inflammation but otherwise share the same clinical features, response to treatment, and coronary outcomes as patients without arthritis.Most cases of arthritis resolve without additional therapeutic intervention. Objective: To define the prevalence, pattern, and clinical course of arthritis presenting at the time of diagnosis of Kawasaki disease. Study design: A single-center, retrospective study of 414 consecutive patients diagnosed with Kawasaki disease between January 1997 and December 2002 was performed . Standardized clinical assessments, laboratory and imaging test results, and treatment regimens were reviewed. The clinical, laboratory, treatment response, and coronary outcome data were analyzed for children with and without arthritis. Results: The prevalence of arthritis was 7.5% (31 / 414). In the 31 children with arthritis, 55% had oligoarticular involvement and 45% had polyarticular involvement. Some 88% of the children with arthritis responded to standard intravenous immunoglobulin therapy for acute Kawasaki disease and did not require additional medications. The children with arthritis had significantly increased levels o f inflammatory markers, but their demographical and clinical features were otherwise similar to those of the children without arthritis, including coronary outcome, with the same proportion (13%) of children from each group with coronaryartery lesions (z-score ≥2.5). Conclusions : Children with arthritis have evidence of acute systemic inflammation but otherwise share the same clinical features, response to treatment, and coronary outcomes as patients without arthritis. Patients with arthritis resolve without additional therapeutic intervention.