Criteria for the classification of juvenile rheumatoid arthritis were analyzed in a detailed database of 250 children in order to assess the accuracy of diagnosis and validity of onset types and course subtypes. A number of conclusions have been derived from this study: 1) All definitions of the 1973 criteria for classification of juvenile rheumatoid arthritis should be retained. 2) The addition of onset types to the 1976 revision of the criteria has been validated. 3) The course of the disease after the onset period of 6 months is as important to the outcome of a group of children as is the onset type. 4) The current classification should be broadened to include the course subtypes.