In this prospective randomized study, we compared humeral block (HB) and infraclavicular brachial plexus block (ICB) with pain caused by the block as a primary outcome, assuming that ICB would cause less pain than HB. Patients undergoing emergency upper limb surgery were included in this study and received either ICB (group I, n = 52 patients) or HB (group H, n = 52 patients). Patients were asked to quantify the severity of the pain during the procedure using a visual analog scale from 0 to 100 mm and to identify which of the 4 components of the procedure was most unpleasant (skin transfixion, needle redirection in search of the nerves, local anesthetic injections, or electrical stimulation). The block was assessed every 5 min for 30 min after completion of the block. Overall visual analog scale scores for the block were 35 +/- 27 mm in group H versus 19 +/- 18 mm in group I (P < 0.0011). Electrical stimulation was the most unpleasant part of the block (group H, 29 +/- 15 mm versus group I, 15 +/- 10 mm) (P < 0.019). Time to perform the block was significantly shorter in group I (ICB, 6 +/- 4 min versus HB, 10 +/- 4 min; P < 0.0001). The onset time was 13 +/- 7 min for ICB and 9 +/- 3 min for HB (P < 0.05). No serious complications were observed. In summary, ICB is less painful, compared with HB, with a similar success rate.