Sera of 12 patients with complex regional pain syndrome (CRPS) were tested for the occurrence of autoantibodies against nervous system structures. Immunohistochemistry revealed autoantibodies against autonomic nervous system structures in 5 of 12 (41.6%) of the patients. Western blot analysis showed neuronal reactivity in 11 of 12 (91.6%) patients. The authors hypothesize that CRPS can result from an autoimmune process against the sympathetic nervous system.