Erythromelalgia is a rare condition that has remained an enigma diagnostically and therapeutically for decades. It has been assumed that erythromelalgia, which is characterized by hot, red, intensely painful feet or hands, may be the opposite of Raynaud's phenomenon. However, new research suggests that these two disorders are more similar than dissimilar. Erythromelalgia usually follows a chronic, sometimes progressive and disabling course. New evidence suggests that this may not be a disease entity at all, but a syndrome of dysfunctional vascular dynamics; recent studies demonstrate that this dysfunction is reversible in some patients. This review article presents the latest theories and successful treatments for erythromelalgia, and data from a survey of members of The Erythromelalgia Association, which was formed to provide information about erythromelalgia to doctors and patients. (J Am Acad Dermatol 2000;43:841-7.)