We studied the effects of local anesthetic volume on diaphragmatic excursion after ultrasound-guided interscalene brachial plexus block (ISBPB). Twenty patients underwent ultrasound-guided ISBPB for pain in the upper extremity, shoulder, or neck with either 10 ml (n=10) or 20 ml (n=10) of 1% mepivacaine. Diaphragmatic excursion during quiet and deep inspiration was assessed by ultrasonography before and after ISBPB. All patients had hypoalgesia of at least C5-7. There was no significant change in diaphragmatic excursion in the 10 ml group, while a significant decrease was observed in the 20 ml group. We concluded that diaphragmatic excursion is preserved after ultrasound-guided ISBPB with 10 ml of 1% mepivacaine.