Introduction: The purpose of the study was to find the complications in post-operative patients of peritonitis using Mannheim’s Peritonitis index. An observational study conducted in a 60 patiens at tertiary care centre as emergency cases of perforation. Patients with clinical suspicion and investigatory support for the diagnosis of peritonitis (diffuse or localised) due to hollow viscous perforation who are later confirmed by intra- operative findings were included in study. Quantitative data was tested by Mean and Standard Deviation, difference between two means tested by ’Z’ test. Qualitative data was compared by Chi square test, Fisher’s exact test. P value <0.05 was considered significant. Conclusion:  it seems that most peritonitis cases were of non-colonic sepsis origin and presented late I.e. after 24 hours of perforation, had to be managed with exploratory laparotomy and primary Closure. In the present study, recovery rate was 86.67% and death rate was 13.33%. MPI score of <21 was significantly more associated with recovery (p=0.0008) hence we observed more recovery rate, as most of the patients in our study had MPI score of <21. MPI score of >29 was significantly more associated with deaths (p=0.0001), hence we have observed deaths among those patients who had high MPI scores. So MPI (Mannheim Peritonitis Index) can be used for assessing severity and predicting prognosis of the peritonitis patients.