THE SUBJECT of this paper is a term uncommonly used and poorly understood, not only by the medical profession in general but also by the physicians and surgeons interested in painful extremities. It is a term that may be rightfully discarded within a few years when a better understanding of the syndrome is obtained. For the present, however, it signifies, as well as any term, pain in an extremity that may be relieved by interruption of regional efferent sympathetic fibers. Such terms as Sudeck's atrophy, causalgia-like state, post-traumatic painful osteoporosis, reflex dystrophy of the extremities and minor causalgia have been used to designate this syndrome. Sympathetic dystrophy has been compared to causalgia. The latter term, however, refers to the syndrome first described by Mitchell, Morehouse and Keen1 and implies a burning type of pain not confined to the distribution of a peripheral nerve and occurring after trauma to one