BACKGROUND This study compared the characteristics of hyperbaric and hypobaric bupivacaine in patients undergoing unilateral lower limb surgeries under lumbar subarachnoid block with regard to their onset and level of sensory and motor blockades, haemodynamic stability, and recovery profile in terms of analgesic duration and motor recovery. METHODS This is a comparative study. Two groups, each of 36 patients who satisfied American society of Anaesthesiologist (ASA) I & II aged 18 – 65 years, were observed intra operatively and during immediate post-operative period. Group 1 received 2.4 ml of 0.5 % bupivacaine (heavy) with operated limb in dependent position. Group 2 received 4 ml of reconstituted hypobaric bupivacaine 0.3 %, with the operated limb positioned in non-dependent position. Onset, level and duration of motor and sensory block, hemodynamic changes and duration of surgical analgesia were compared between groups. RESULTS The level of sensory block attained in the hypobaric group was at T12 with maximum at T9, in the hyperbaric group it is variable and at higher level. Duration of sensory blockade was less with hypobaric. Motor block of modified Bromage scale 3 after 10 minutes was none in group 2 and 91.7 % in group 1. Significant fall in systolic blood pressure at 15 to 30 minutes and diastolic BP at 15 and 20 minutes was noted in hyperbaric group after subarachnoid block. There was significant percentage of change in systolic blood pressure from 4 to 70 minutes and mean arterial pressure (MAP) from 4 to 90 minutes in hyperbaric group. Duration of surgical analgesia in hypobaric group was longer compared to hyper baric. CONCLUSIONS Intrathecal hypobaric bupivacaine showed better haemodynamic stability and longer duration of analgesia in comparison with hyperbaric bupivacaine in lower limb surgeries. KEYWORDS Anaesthesia, Bupivacaine, Hypobaric, Subarachnoid Block