50 patients undergoing unilateral arthroscopic knee surgery were randomized to either receive 10 mg of 0.5% hyperbaric bupivacaine or 5 mg 0.5% hyperbaric bupivacaine combined with 2.5 micro grams of sufentanil to obtain unilateral spinal anesthesia. The objective of this trial was to compare efficacy of the combinations for unilateral spinal anesthesia. Assessments measured over 24 hours indicated that the combination of bupivacaine with sufentanil provided a quicker sensorial block, lowered the possibility of motor block in unilateral spinal anesthesia, and may reduce the number of patients requiring analgesia to ease post-operative pain.