Seventy patients suffering from purulent peritonitis entered this study, 31 of them were taken in prospectively, to contrast two different prognostic scores, the Mannheim Peritonitis Index (MPI) vs. the Apache II (APS II). The MPI is shown as a prognostic index for peritonitis with high accuracy in individual prognosis. The simultaneous use of both scores, the MPI as well as the APS II, leads to a negligible improvement of prognostic accuracy. Moreover, sensitivity and specificity with the MPI are of higher accuracy than calculated with the APS II.