Background: Changes in tissue oxygen saturation determined by near-infrared spectroscopy (NIRS) may help predict and determine the success of a lateral infraclavicular (LIC) block. We investigated whether evaluation of tissue oxygen saturation determined by NIRS could be an indicator of LIC block success. Methods: Forty patients scheduled for hand or forearm surgery under LIC block were studied. NIRS sensors were placed on the ventral aspect of both mid-forearms, and the contra-lateral hand was used as the control group. NIRS values were recorded before the block and at regular intervals during the following 30 min. Results: NIRS values were significantly higher in the successfully blocked patients when compared to the complete failure, partial failure, and contralateral hand groups at the 10th min. In the successfully blocked patients, NIRS values (mean ± SD [change in %]) increased by 11.09 ± 4.86 (16.03%), 15.00 ± 4.53 (21.76%), 16.35 ± 5.14 (23.77%), 16.38 ± 4.88 (23.85%), 16.67 ± 5.04 (24.29%), and 16.96 ± 5.71 (24.78%), respectively, from baseline to 5, 10, 15, 20, 25, and 30 min. ΔTs values were significantly higher in the successfully blocked patients than in the complete failure patients and contralateral hand at the 30th min. However, there was no statistically significant difference when comparing ΔTs values of successful block and partial failure block patients at the 30th min. Conclusions: We conclude that measurement of tissue oxygen saturation by NIRS within the scope of evaluation of the lateral infraclavicular block is a rapid, effective, and applicable technique.