One hundred eighty-seven patients treated for established intra-abdominal infection in five medical centers were studied using the surgical infection stratification system. This system combines an anatomic category with a numerical estimate (acute physiology score [APS]) of deviation from normal of 33 routine laboratory tests or physical findings. Overall mortality was 24% and the rate of treatment "success" with a single operation and single course of antibiotics was 48%. Eighty percent of deaths occurred with infection present. Multivariate analysis disclosed that APS, malnutrition, and age were most noteworthy for predicting survival or death. Intra-abdominal infection carries substantial mortality and morbidity despite advances in understanding the underlying pathophysiologic condition. Additional clinical studies are needed. Uniform reporting criteria, including the use of an objective severity scoring system, are suggested for future reports concerning intra-abdominal infection.