For many years a united international classification for chronic childhood arthritis has been absent. The lack of consensus has led to difficulties in trial structure and data interpretation. The authors put forward the new ILAR classification in which the term JIA replaces JRA and JCA. The classification is based on clinical characteristics during the first 6 months of disease and divided into seven distinct categories. The ILAR classification aspires to define categories of arthritis that are clinically homogenous such that to a degree this may predict response to therapy and outcome. A detailed account of the new classification and possible pitfalls is given.