Still's disease is a form of juvenile idiopathic arthritis, characterized by high spiking fevers and transient rashes, named after the English physician Sir George Frederic Still (1861-1941). The disease was first discovered in children, but now it is also known to occur, less commonly, in adults in whom it is referred to as adult-onset Still's disease.

There are several theories about the cause of Still's disease. It has been suggested it may be caused by a microbacterial infection or that it is an autoimmune disorder. However, the cause of Still's disease remains unknown