To estimate the number of children with rheumatic diseases, a questionnaire was distributed to the pediatrics department of 1,290 hospitals in Japan in June 1994. From this survey, 1,606 cases with juvenile rheumatoid arthritis (JRA), 906 cases with systemic lupus erythematosus (SLE), 320 cases with dermatomyositis/polymyositis (DM/PM), 28 cases with scleroderma (PSS), 70 cases with Sjögren's syndrome (Sjs), 93 cases with mixed connective tissue disease (MCTD), 25 cases with aortitis syndrome, 20 cases with polyarteritis (PN) and 51 cases with Behçet disease were reported. The crude annual incidence rates per 100,000 among the childhood population were estimated as JRA, 0.83; SLE, 0.47; DM/PM, 0.16; PSS, 0.01; Sjs, 0.04; MCTD, 0.05; aortitis syndrome, 0.01; PN, 0.01; and Behçet disease, 0.03. The present study reveals that there are more children with rheumatic diseases than are estimated from the reported cases in the literature and the number of children who are receiving Assistance Medical Costs Insurance covered by the Japanese government.