Aim: To study the frequency of hypocalcemia in patients admitted to an intensive care unit and whether hypocalcemia has any correlation with disease severity measured by acute physiology and chronic health score APACHE II. Materials and methods: The prospective study was carried out in Chattrapati Shivaji Subharti Hospital, Meerut in the Department of Medicine among 100 critically ill patients who were admitted in the ICU. The patients underwent a detailed history including past, treatment and personal history to identify possible aetiologies and a thorough clinical examination to identify the hypocalcemia. Demographic information, clinical information and the (APACHE) II score was collected and patients were followed up to determine mortality. Ionized calcium (iCa), pH and lactate results was obtained from blood gas analysis on whole arterial blood collected in heparinized syringes. Results: Burn, cardiac, medical, neurology, respiratory and trauma was revealed among the 12%, 6%, 41%, 18%, 12% and 11% of the subjects respectively. Normal calcium level was found among 43% of the subjects while hypocalcemia was reported among 57% of the subjects. It was found that APACHE II score increases with decrease in calcium level. Mortality was revealed among 13.95%, 14.82%, 42.86% and 43.85% of the subjects having normocalcaemic, mild, moderate and severe hypocalcemic level. Conclusion: In this study, severely hypocalcemic patients on admission whose calcium failed to rebound to normal trended towards having a higher mortality and may be a target for intervention.