Background: Mannheim Peritonitis Index, that has been evaluated to calculate the prognosis of the peritonitis patients, is a simple and predictive scoring test. The disadvantage is that some of the parameters must be calculated peroperatively. In our studies, in order to by-pass this disadvantage, by modificating the test by the bladder pressure parameters thus creating a new scoring system that's called Modificated Mannheim Peritonitis Index. Material and method: Seventy-five patients, between the age of 15-89, diagnosed as surgical acute abdominal syndrome and planned to have an emergency operation has been included in the study. Results: It has been found out that the Mannheim Peritonitis Index score of the patients, increases with the length of hospitalitisation. If the test cut-off value is set to 26, the scores above this level shows increased the postoperative complications and mortality rates. Mannheim Peritonitis Index score above 30 are calculated to have a sensitivity of 57%, specificity of 82%, positive predictive value of 25% and negative predictive value of 95% and a 80% accuracy rate for predicting the mortality. We also found that the bladder pressure on admission is irrevelant on mortality and complication rates. The prognosis of the patients has a statistically significant relationship with the parameters: Age above 50, organ failure, malignancy, sepsis and exudate with feces. Conclusions: As an addition the goal as changing some of the parameters of Mannheim Peritonitis Index with bladder pressure values and creating a new scoring system with similar predictive abilities has been failed.