The purpose of this study was to evaluate and compare the hemodynamic and respiratory changes in patients undergoing unilateral and bilateral spinal anaesthesia. Subject and method: 60 elderly patients with age ranging from 65 to 90, ASA I, II, II whom were scheduled for lower limb surgery were randomly allocated in to two groups, each had 30 patients. Both groups underwent spinal anesthesia with 0.5 percent hyperbaric bupivacaine 0.12 mg/kg combining with fentanyl 0.03 mg. Group I underwent unilateral anaesthesia and group II underwent bilateral spinal anaesthesia. Parameters used for statistical analysis and comparison were blood pressure, heart rate, respiratory parameters, duration of sensory block and side effects. Result and conclusion: Rate of excellent anesthesia was 100 percent in group I and 83.4 percent in group II. Mean arterial blood pressure at 5, 15 and 30 minutes after injection of group II were significantly lower than that of group I. Heart rate, respiratory rate and saturation of oxygen did not differ between the groups. Side effects such as hypotension and bradycardia were more common in group II whereas the duration of sensory block in group I was significantly longer than group II.