peritonitis and mortality and morbidity regarding it is very common situation for surgeons, pre–operative prognostic scoring like POSSUM allows surgeon to predict the post–operative outcome which can be used in for better patient’s counseling, improving surgical outcome and better management of limited resources and man power. objective: To predict the prognosis and outcome of the patients with peritonitis based on the POSSUM score and correlation between the POSSUM score and the severity of the disease. Data collected prospectively from 100 consecutive patients of peritonitis admitted at surgical wards to compare POSSUM score for morbidity and mortality with complications and outcome. mean age was 39.33±18.48 years, perforations of the peptic ulcers are the most common cause of peritonitis forming 34% of the study, The most common complication was septicemia (29%) ,Wound dehiscence (24.13%) was the most common complication in survived patients . The overall O:E ratio for POSSUM morbidity and mortality score were 0.93 and 1.21,in the ROC curve, higher number of complications and morbidity was observed with POSSUM morbidity score of >95.8% and the AUC being 0.987.ROC curve for mortality, the increase incidence of deaths were observed for score of >59.1% with AUC being 0.987 .the study showed a highly significant statistical difference, p value <0.0001 between the survived and expired patients and the POSSUM morbidity and mortality scores .Thus to summarize, POSSUM score is easier, faster and convenient in estimating morbidity and mortality in cases of peritonitis undergoing surgery.