Perfusion Index (PI) is a relatively new parameter tried for predicting hypotension . This study aimed at investigating correlation between baseline PI and incidence of hypotension following Sub–arachnoid block (SAB) . In this prospective & observational study , patients were divided into 2 groups on the basis of baseline PI. Group I with PI < 3.5 and Group II PI > 3.5. SAB performed with 15 mg of 0.5% (H) bupivacaine at L3–L4 inter–vertebral space. The incidence of hypotension in group I (PI< 3.5) was 10.71% compared to 68.97% in group II (PI > 3.5). There was significant correlation between baseline PI and number of episodes of hypotension . The ROC (Reciever Operating Characteristic) curve analysis revealed that baseline PI was suitable for detecting patients at risk for hypotension . For predicting hypotension , perfusion index (PI) can be used as a tool in patients undergoing below umbilical surgeries for SAB . Patients with baseline PI >3.5 have higher chances of developing hypotension than patients with PI <3.5.