BACKGROUND: This study was performed to evaluate the therapeutic effects of sympathetic block in management of reflex sympathetic dystrophy (RSD); renamed complex regional pain syndrome (CRPS) Type I, according to the duration of RSD, and to evaluate predictable factors responding to sympathetic block in patients suffering from RSD. METHODS: Prospectively designed this study was divided thirty patients with upper extremity RSD into three groups according to the duration of RSD; Group I (< or = 3 months), Group II (4 to 6 months) and Group III (>or = 7 months). All patients were received repeated stellate ganglion blocks (SGB) with 12 ml of 0.2% bupivacaine by paratracheal approach. We compared the therapeutic effects of SGB between the groups and the clinical signs on initial examination to receive the first SGB at pain clinic. RESULTS: Response rates to SGB were 84.6% in Group I, 62.5% in Group II and 44.4% in Group III. The early treatment less than 6 months was better prognosis (p<0.05). Presence of edema (p<0.001), temperature differences between both hands (hot>cold>no difference, p<0.001), and allodynia (p<0.05) were favorable prognostic factors responding to sympathetic block. Especially, warm skin and edema in RSD were near-perfect predictors of sympathetic blocks. CONCLUSIONS: We conclude that SGB is effective in management of upper extremity RSD, and the duration and the clinical signs of RSD are important to the prognosis and responsibility to sympathetic block. If patients suffering from RSD visit pain clinic before 6 months, and they have edematous warm hands with allodynia, majority of them will be improved from their pain after sympathetic block.