Background The adjunction of ultrasound to nerve stimulation has been proven to improve single-injection peripheral nerve block quality. However, few reports have been published determining whether ultrasound can facilitate continuous nerve blocks. In this study, we tested the hypothesis that the addition of ultrasound to nerve stimulation facilitates femoral nerve blocks with a stimulating catheter.Methods In this prospective randomized study, patients receiving continuous femoral nerve blocks for total knee replacement were randomly assigned to either the ultrasound guidance combined with stimulating catheter group (USNS group; n=60) or the stimulating catheter alone group (NS group; n=60). The primary end point was the procedure time (defined as the time from first needle contact with the skin until correct catheter placement). The numbers of needle passes and catheter insertions, onset and quality of femoral nerve blocks, postoperative pain score, and early knee function were also recorded.Results The procedure time was significantly less in the USNS group than in the NS group (9.0 (6.0-22.8) minutes vs.13.5 (6.0-35.9) minutes, P=0.024). The numbers of needle passes and catheter insertions were also significantly less in the USNS group. A greater complete block rate was achieved at 30 minutes in the USNS group (63.3% vs. 38.3%;P=0.010). The postoperative pain score, the number of patients who required bolus local anesthetic and intravenous patient-controlled analgesia, and knee flexion on the second postoperative day were not significantly different between the two groups of patients.Conclusions Ultrasound-assisted placement of a stimulating catheter for femoral nerve blocks decreases the time necessary to perform the block compared with just the nerve-stimulating technique. In addition, a more complete blockade is achieved using the ultrasound-assisted technique.