Early prognostic evaluation of abdominal sepsis is desirable to select high-risk patients for more aggressive therapeutic procedures and to provide objective classification of the severity of disease. The reliability of the Mannheim peritonitis index was assessed and its predictive power for different populations examined in a study of 2003 patients from seven centres in three European countries. The prevalence of risk factors varied considerably between the groups. For a threshold index score of 26, the sensitivity was 86 (range 54–98) per cent, specificity 74 (range 58–97) per cent and accuracy 83 (range 70–94) per cent in predicting death. For patients with a score less than 21 the mean mortality rate was 2.3 (range 0–11) per cent, for score 21–29 22.5 (range 10.6–50) per cent and for score greater than 29 59.1 (range 41–87) per cent. The mean index score and mean mortality rate correlated in the different groups, reflecting a homogeneous standard of therapy for peritonitis. The Mannheim peritonitis index provides an easy and reliable means of risk evaluation and classification for patients with peritoneal inflammation.