One hundred forty-five consecutive three-phase radionuclide bone scans were reviewed. One hundred two of these were performed to evaluate pain in the hand. Of these, 23 patients clinically had reflex sympathetic dystrophy (RSD). The hand scans were performed by the three-phase technique. Phase I is a radionuclide angiogram. Phase 11 is the blood pool or tissue phase. Phase III consists of delayed images obtained 3 to 4 hours after radionuclide injection. Detailed analysis of the 145 three-phase radionuclide bone scans of the hand demonstrated that the diffuse increased tracer uptake in the delayed image (phase III) is diagnostic for RSD, with a sensitivity of 96% and a specificity of 98%. The two early phases (radionuclide angiogram and blood pool) were positive in only 45% and 52% of the RSD patients, respectively. The strictly interpreted delayed radionuclide image is extremely sensitive in the diagnosis of RSD and will facilitate the early diagnosis and subsequent treatment of this syndrome.