Block of the sciatic nerve at the midfemoral level is usually performed using nerve stimulation techniques. We investigated the efficacy of ultrasound, combined with nerve stimulation, to locate and block the sciatic nerve at the lateral midfemoral level compared to nerve stimulation alone. Sixty-one patients scheduled for foot and ankle surgery were enrolled in this prospective, randomized study. Thirty patients underwent a lateral block of the sciatic nerve at the midfemoral level guided by ultrasound (group US) and 31 patients received the block without ultrasound (group ES). Once an adequate motor response was obtained using nerve stimulation, 35 mL of ropivacaine 0.5% was administered. The main end-points of the study were: number of attempts to obtain an adequate motor response, success rate of nerve location at the first attempt, quality and duration of both sensory and motor blocks, and anesthetic distribution. The success of sciatic nerve location at the first attempt was significantly more frequent in the US group than in the ES group (76.6% versus 41.9%; P < 0.001). The quality of the sensory block and the tolerance to the pneumatic tourniquet were also significantly better in the US group (P < 0.01). We conclude that ultrasound combined with nerve stimulation improved the quality of the sensory block and the tolerance to the pneumatic tourniquet, reducing the number of attempts to perform sciatic nerve block at the midfemoral level.