Background: The majority of procedures involving the abdomen and lower limbs are best performed under regional anesthetic. This study evaluated the effects of intravenous dexmedetomidine on spinal anesthesia with 0.5% hyperbaric bupivacaine. Materials & Methods:90 patients scheduled for orthopedic lower limb surgeries under sub arachnoid blocks were divided into 2 groups of 45 patients each. Drugs for both groups prepared in two 50 ml syringes- one for loading dose (labelled L) and the other for maintenance dose (labelled M). Results: Group I had 25 males and 20 females and group II had 23 males and 22 females. The mean duration of onset of sensory blockade was 7.2 minutes in group I and 6.1 minutes in group II. The duration of onset of motor blockade was 3.1 minutes in group I and 3.3 minutes in group II. The duration of recovery from sensory blockade was 215.0 minutes in group I and 161.5 minutes in group II. The duration of recovery from motor blockade was 238.2 minutes in group I and 195.4 minutes in group II. The sedation score was 2.7 in group I and 3.5 in group II. The difference was significant (P< 0.05). The pain score (VAS) in group I and II was 2.3, 3,2 respectively. At 2 hours, it was 1.6 and 4.6, at 6 hours was 2.4 and 5.1, at 12 hours was 2.4 and 5.1 and at 24 hours was 2.1 and 6.2 respectively. The difference was significant P< 0.05). Conclusion: Arousable sedation produced by subarachnoid anesthesia is prolonged by intrathecal dexmedetomidine.