A 60-year-old morbidly obese woman (150 cm, 112 kg, BMI 49.8) underwent total knee replacement under general anesthesia combined with sciatic nerve block and continuous femoral nerve block. Following induction of general anesthesia and tracheal intubation, the sciatic nerve was blocked using the popliteal approach with the patient in the supine position. Then the femoral nerve block was performed, followed by perineural catheter placement for postoperative continuous local anesthetic infusion. For both procedures, real-time ultrasound imaging was used to facilitate needle placement and confirm the adequate local anesthetic deposition. Twenty-five and 30 ml of 0.375% ropivacaine was injected around the sciatic and femoral nerves, respectively. Postoperatively 0.15% ropivacaine was infused at the rate of 5 ml x hr(-1) for 60 hours through the femoral catheter, which provided satisfactory pain relief in combination with scheduled loxoprofen administration. No block-related complications were noted. Our experience suggests that the ultrasound-guided technique may prove useful to facilitate safe and accurate block when technical difficulties are anticipated with anatomic landmark-based approaches.