The objective of this study was to define risk factors for and the clinical course of recurrent or tertiary peritonitis. Intensive supportive care of patients with life-threatening intraabdominal infections has led to the emergence of a new clinical syndrome, tertiary peritonitis, defined as the persistence or recurrence of intraabdominal infection following apparently adequate therapy of primary or secondary peritonitis. We undertook a retrospective study of 59 patients admitted with intraabdominal infection to a surgical intensive care unit (ICU). Tertiary peritonitis developed in 74% (44/59) of patients. Despite comparable premorbid health status, source of peritonitis, and admission APACHE II scores, patients with tertiary peritonitis had a significantly longer ICU stay (21.8 +/- 14.9 vs. 8.5 +/- 7.9 days), more advanced organ dysfunction reflected in higher organ dysfunction scores (13.3 +/- 5.1 vs. 7.7 +/- 3.3), and higher ICU mortality (64% vs. 33%) than patients with uncomplicated secondary peritonitis. The most common infecting organisms in patients with tertiary peritonitis were Enterococcus, Candida, Staphylococcus epidermidis, and Enterobacter. Infectious foci were rarely amenable to percutaneous drainage and were found to be poorly localized at laparotomy. Recurrent, or tertiary, peritonitis is a common complication of intraabdominal infection in patients admitted to an ICU. It differs from uncomplicated secondary peritonitis in its microbial flora and lack of response to appropriate surgical and antibiotic therapy. Like nosocomial pneumonia in the critically ill patient, the syndrome appears to be more a reflection than a cause of adverse outcome.