The epidemiology of juvenile idiopathic arthritis (JIA) is variable worldwide. In particular, a wide disparity exists in the prevalence of the diverse disease subtypes across different geographic areas. The therapeutic approach to JIA is not standardized and no established and widely accepted guidelines are available. In the past decade, there have been important progresses in the management of the disease, but the availability of the novel and costly biologic medications is not uniform throughout the world. This issue may have significant impact on disease prognosis, with children living in poorer countries being at greater risk of accumulating disease- and treatment-related damage than children followed in Western pediatric rheumatology centers. The multinational study of the EPidemiology, treatment and Outcome of Childhood Arthritis (EPOCA study) is aimed to obtain information on the frequency of JIA subtypes in different geographic areas, the therapeutic approaches adopted by pediatric rheumatologists practicing in diverse countries or continents, and the disease and health status of children with JIA currently followed worldwide. Parent- and child-reported outcomes are meant to be recorded through the administration of a new multidimensional questionnaire, the Juvenile Arthritis Multidimensional Assessment Report (JAMAR). The first step of the study is based on the translation and cross-cultural adaptation of the questionnaire in the national language of each participating country. Each center is, then, asked to enroll a sample of consecutive JIA patients, who should undergo a retrospective assessment and a cross-sectional evaluation, including completion of the JAMAR, a standardized joint examination, and the assessment of articular and extra-articular damage. At the end of May 2012, 124 centers in 55 countries have agreed to participate in the study. The JAMAR has been or is currently being translated in 38 national languages. The target patient sample is more than 10,000 JIA children worldwide.