Introduction: Sepsis is a life-threatening condition of human body. It is caused by improper response of host immune system to various infective conditions. Procalcitonin (PCT) has been a promising biomarker for aiding early diagnosis, risk stratification and treatment in patients with sepsis and septic shock. Aim: To study correlation of serial serum procalcitonin (day1, 3 and 7) with severity of sepsis and patient outcomes (in-hospital stay or mortality). Materials and Methods: The study was a descriptive, observational study conducted at Krishna Institute of Medical Sciences, Secunderabad, Telangana, India, on 100 patients admitted to Medical Intensive Care Unit (MICU), both males and females of age more than 18 years, with sepsis or septic shock, from August 2019 to January 2021. Serum procalcitonin was measured by BRAHMS PCT-Q immunochromatographic assay using a commercially available test kit. Blood, urine and wound cultures were performed to confirm specific infection. The Chisquare test, Fischer’s-exact test and Pearson correlation tests were used to calculate association and correlations amongst qualitative data. Results: Total 100 patients (mean age was 49.9±17.0 years; 62 males and 36 females) were included in the study. A total of 74 patients were observed to be have sepsis and 26 patients Ihad septic shock. Mortality was 36%. There was a positive correlation with Sequential Organ Failure Assessment (SOFA) score on day 1 and 3, but not day 7. PCT was high in 85% of patients on admission (day 1). Higher levels of PCT was observed both in patients with sepsis (82.4%) and septic shock (92.3%), suggesting that it is a good diagnostic marker in these patients. Mean PCT was higher in death patients compared to discharged patients on day 1,3 and 7 (p-value<0.05). Majority of patients (71.8%) with higher PCT on admission stayed in ICU for less than 5 days, whereas over half (53.3%) with normal PCT had a short ICU stay (p-value=0.18). Conclusion: Procalcitonin is a useful marker for early diagnosis of sepsis and septic shock and also severity of infection on admission to ICU. High procalcitonin also predicts mortality and can be a useful tool for rational use of antibiotics in patients admitted to ICU.