BACKGROUND: Several methods are performed to control the pain after a laparoscopic cholecystectomy. Recently, the transverse abdominis plane block has been proposed to compensate for the problems developed by preexisting methods. This study was designed to evaluate the effect of the ultrasound-guided transverse abdominis plane block (US-TAP block) and compare efficacy according to the concentration of local analgesics in patients undergoing laparoscopic cholecystectomy. METHODS: Fifty-four patients undergoing laparoscopic cholecystectomy were randomized into three groups. The patients in Group Control did not receive the US-TAP block. The patients in Group B(0.25) and Group B(0.5) received the US-TAP block with 0.25% and 0.5% levobupivacaine 30 ml respectively. After the general anesthesia, a bilateral US-TAP block was performed using an in-plane technique with 15 ml levobupivacaine on each side. Intraoperative use of remifentanil and postoperative demand of rescue analgesics in PACU were recorded. The postoperative verbal numerical rating scale (VNRS) was evaluated at 20, 30, and 60 min, and 6, 12, and 24 hr. Postoperative complications, including pneumoperitoneum, bleeding, infection, and sleep disturbance, were also checked. RESULTS: The intraoperative use of remifentanil, postoperative VNRS and the postoperative demand of rescue analgesics were lower in the groups receiving the US-TAP block (Group B(0.25) and Group B(0.5)) than Group Control. There were no statistically or clinically significant differences between Group B(0.25) and Group B(0.5). No complications related to the US-TAP block were observed. CONCLUSIONS: The US-TAP block with 0.25% or 0.5% levobupivacaine 30 ml (15 ml on each side) significantly reduced postoperative pain in patients undergoing laparoscopic cholecystectomy.