The number of published pediatric studies on the use of transversus abdominis plane (TAP) block has increased in recent years. The transversus abdominis plane (TAP) block has been used for postoperative analgesia for surgery to the abdominal wall and involves the injection of local anesthetic solution into a plane between internal oblique (IO) and transversus abdominis (TA) muscles. The TAP block has the advantage of providing unilateral analgesia in instances of non-midline abdominal incision and is particularly useful in cases where epidural blockade is either contraindicated or technically or logistically not feasible. Bupivacaine and ropivacaine have been used as local anesthetics for TAP blocks in published studies to date. However, no data exist regarding the pharmacokinetics of bupivacaine after TAP block in children. The aims of this study are to determine population pharmacokinetic (PK) parameters of bupivacaine in children following a TAP block, using a population-based PK approach.