A nerve stimulation-guided lumbar plexus block is a well-established technique. It is not clear whether ultrasound guidance has additional value for this deep block technique. This study aimed to examine whether ultrasound guidance using a paramedian transverse scan through the intertransverse space ( PMTS-ITS) approach in combination with nerve stimulation reduces the onset time of a complete sensory block. Forty-four patients who were scheduled to undergo arthroscopic knee surgery with an ultrasound visibility score (UVS) of >= 10 for the lumbar plexus were enrolled and randomly allocated to the ultrasound guidance with nerve stimulation group (group U-N) or nerve stimulation group (group N) in this prospective, randomized, parallel-group, active-controlled study. The primary outcome was the onset time of a complete sensory block. The results showed that the onset time of a complete sensory block to pinprick and cold was 10 (10-40) min and 10 (10-40) min in group U-N, respectively, and 30 (10-40) min and 20 (10-40) min in group N (P=0.005, P=0.004), respectively. The performance time was 658 +/- 87 s in group U-N and 528 +/- 97 s in group N (P<0.001). There was no (0%) patient who required 5 or more needle passes in group U-N and 6 (27.3%) in group N (P=0.028). The block failure rate was 9.1% in group U-N and 31.8% in group N (P>0.05). In conclusion, ultrasound guidance using the PMTS-ITS approach in combination with nerve stimulation led to a faster onset of a complete sensory block than nerve stimulation alone for a lumbar plexus block in patients with a UVS >= 10. Ultrasound guidance with nerve stimulation significantly decreased the number of patients who required 5 or more needle passes.