Scoring systems are mandatory to quantify the severity of abdominal sepsis on the basis of objective criteria. The Mannheim Peritonitis Index (MPI) is a disease-specific score based on easy to handle clinical parameters. APACHE II is a large-scale general scoring system with acute physiological and chronic health parameters. To evaluate the prognostic value of both systems 108 patients with severe abdominal infection managed by open treatment entered a prospective study. 32 patients (29.6%) died, 23 of them due to sepsis and 9 from other causes. Both MPI and APACHE II scores correlated closely with mortality, with three and two significantly different classes, respectively. Statistical validation showed a sensitivity of 93% and a specificity of 16% for MPI, and 89% and 25% for the APACHE II. ROC curves were nearly parallel for both scores. In conclusion there was no significant difference in prognostic value between the scoring systems.