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Background & Objectives: Ultrasound-guided (USG) peripheral nerve block allows for visual verification of the relationship between sciatic nerve and local anesthetic (LA). Nerve stimulation guidance may help to prevent intraneural injection of LA. This clinical investigation aimed to estimate the minimum effective anesthetic volume (MEAV) of ropivacaine 0.5% required to block the sciatic nerve at subgluteal injection under guidance of ultrasound with nerve stimulation in 90% patients. Materials & Methods: Patients with an American Society of Anesthesiologists physical status I-II who were scheduled for arthroscopic meniscus or cruciate ligaments repair of knee were eligible for study inclusion. All patients underwent blockade of both the lumbar plexus as well as the sciatic nerve using ultrasound and nerve stimulation to identify nerve location. Sixteen ml 0.5% ropivacaine was administered to the first patient for sciatic block. Dosing of subsequent patients was determined using Dixon and Massey up-and-down sequential method. After administration of the anesthetic, sensory and motor function of the tibial and common peroneal nerve were assessed by a blinded observer. After undergoing the surgical procedure, patients were followed in the hospital for 48 hours. Clinical follow up was continued for one month. Effective volume of ropivacaine 0.5% for sciatic nerve block was calculated using the probit analysis with Dixon’s up-and-down method. Results: Twenty-six patients between the ages of 18 and 48 years old were treated as part of the study. Fifteen patients (58%) had successful sciatic nerve block and 11 had failed block of sciatic nerve. The EV90 of ropivicaine (0.5%) was 13.0 ml (95% CI 12.6–15.0). For all patients VAS at rest was no higher than 2 and VAS at movement was no higher than 4 within the first 48 hours after surgery. At the time of the 1-month follow-up, no neurologic complications were noted. Conclusion: When the sciatic nerve is carefully targeted using both ultrasound and nerve stimulation, successful blockade of the nerve during surgery and appropriate postoperative analgesia is achieved in 90% of patients at a dose of 13.0 mL.