Background: Inflammation of the serosal membrane that borders the abdominal cavity and the internal organs is referred to as peritonitis. Peritonitis typically progresses to a deadly tertiary stage if left untreated or if therapy is unsuccessful. Grading the severity of acute peritonitis has improved therapy and helped with decision-making in the care of critically sick patients.The most often utilized of these are the sepsis severity score, the simplified acute physiology score, and the acute physiology and chronic health assessment score (APACHE II). Materials & methods: In this study a sample size of 75 patients was taken.A Meticulous symptomatic history of all those patients presented with acute abdomen & pre–morbid conditions were well-catalogued accurately along with their general past history.Once the diagnosis of peritonitis was confirmed then the patient’s APACHE II score were assessed categorically within 24 hours of admission.Bilateral flank drainage or conservative management was done to those unfit for surgery.Post–operative outcomes were assessed. Results were processed using SPSS software version 24. Results: Majority of the subjects belonged to 31-40 years (34.7%) followed by > 40 years (33.3%), 21-30 years (25.3%) and 11-20 years (6.7%). Maximum No. of patient were in APACHE 2 score 0-15 (56%) followed by APACHE 2 score 16-30 (37.3%) and least in APACHE 2 score 31-45 (6.7%). Local complications Surgical site infections (18.7%), Prolonged ileus(10.7%), Anastomotic leak(4.0%), Fecal fistula(1.3%) and Intraabdominalabcesss(1.3%) were significantly more among APACHE II scores(31-45) compared to scores (16-30) and (0-15).There was no significant difference in Systemic complications like Sepsis(13.3%), ARDS(5.3%) and Acute renal failure (2.7%) between categories of APACHE II SCORE.Mortality was significantly more in APACHE II score (31-45) as compared to score (16-30) which was significantly more than score (0-15).