Background and Aims: This double blind prospective randomized clinical trial evaluated the efficacy and safety of continuous ultrasound-guided lumbar plexus block compared to continuous ultrasound-guided femoral nerve block, in the intra-operative and postoperative periods after total knee replacement.Methods: Forty ASA I-III patients were randomized to receive: continuous femoral block (n= 20, 30 ml of ropivacaine 5 mg/ml) or continuous lumbar plexus block (n= 20, 30 ml of ropivacaine 5 mg/ml) both in association with single injection sciatic nerve block. All patients received continuous infusion of 2 mg/ml of ropivacaine at 8 ml/h for 48 hours and intravenous morphine for patient-controlled analgesia. Primary outcomes were intra-operative sufentanil consumption and verbal analogue scale (VAS) score at rest at 24h follow up.