Sixty-four consecutive patients were studied for possible reflex sympathetic dystrophy syndrome (RSDS). They were divided into five groups, based upon specific clinical criteria, and the radiographic and scintigraphic findings in each group were examined. Osteoporosis was the most common radiographic abnormality, present in 69% of subjects with definite, probable, or possible RSDS, as compared with 21% opf those with RSDS. Scintigraphic abnormalities were noted in 60% of RSDS patients but in only 7% of the others. These findings included increased blood flow and enhanced periarticular radionuclide activity in the affected extremity. Of 11 patients with serial scintigraphy, six (55%) demonstrated a return to normal, symmetrical patterns following successful therapy. The scan may reflect an active, potentially reversible disorder of local blood flow in RSDS. Furthermore, the scintigraphic patterns may be useful in the diagnosis and in predicting which pattients are likely to respond to systemic steroid therapy.