Juvenile idiopathic arthritis (JIA) is the term used to describe a group of inflammatory articular disorders of unknown cause that begin before the age of 16 and last over 6 weeks. The term juvenile idiopathic arthritis was chosen to signify the absence of any known mechanism underlying the disorder and to highlight the necessity of excluding other types of arthritis occurring in well defined diseases (in particular arthritis occurring in association with infectious, inflammatory and haematooncologic diseases).