BACKGROUND: Horner's syndrome, including ptosis and miosis, is a sign of success following stellate ganglion block (SGB). However, it is not sufficient to ensure adequate sympathetic block to the upper extremity. There are numerous recommended local anesthetic volumes for SGB. The aim of this study was to evaluate the effects of differing volumes used in SGB on the elevation of skin temperature of ipsilateral upper extremity, and to find the volume required to elevate skin temperature most frequently. METHODS: Patients with sensory neural hearing loss underwent SGB, repeated daily in the paratracheal approach using different volumes (6, 8, 10, 12 and 16 ml) of 0.2% bupivacaine. Skin temperatures were checked in the hypothenar area before SGB, and 1, 2, 3, 4, 5, 10 and 15 minutes following SGB. Time intervals required for the elevation of skin temperature 1oC above the preblock level, and for the appearance of Horner's syndrome were recorded. RESULTS: Twenty-three patients repeatedly received SGB over 4 times at different volumes. The total SGB was 100 times, and all displayed Horner's syndrome. The total incidence of skin temperature elevation was 48%. Horner's syndrome appeared prior to the elevation of skin temperature (2.0 2.1 vs 5.3 3.8 min). There were significant differences in the incidence of skin temperature elevation, depending on the volume of the local anesthetics; 6 ml (17.6%), 8 ml (34.8%), 10 ml (52.2%), 12 ml (73.9%) and 16 ml (57.1%); greater volumes resulted in high incidences (pearson chi-square test, P = 0.005). The volume of twelve ml resulted in the highest incidence. Each patient needed different minimal volume to lead to the skin temperature elevation; 6 ml (13.1%), 8 ml (21.7%), 10 ml (17.4%), 12 ml (26.1%) and 16 ml (4.4%), and several patients (17.4%) did not have elevated skin temperature at any volumes. CONCLUSIONS: This study reveals that a large volume of local anesthetic (e.g. 12 ml) is needed in SGB for adequate sympathetic blockade to the upper extremity, and that each patient needs a different minimal volume for the skin temperature elevation to occur.