Aeromonas peritonitis remains a rare condition. In this study we describe the clinical features of primary and secondary Aeromonas peritonitis, and compare the differences between these two diseases entities. Patients with Aeromonas peritonitis were identified from microbiological and medical records during the period between March 1994 and March 2003. Clinical characteristics, laboratory data, microbiological results, treatment and outcome of patients were obtained by retrospective chart review. 22 and 27 patients with primary or secondary peritonitis caused by Aeromonas species were identified. All except two of these patients were adults, with a median age of 62.4 (31-76) vs 65.8 (8-85) years, respectively. Males were predominant (82 vs 78%). Peritonitis was community acquired in 73% and 56% of patients in these two groups, respectively. Significantly higher prevalence of underlying liver cirrhosis (96 vs 7%, p<0.001), which was Child-Pugh class C in 91% of cases, in primary peritonitis was noted. Primary peritonitis was more likely to be monomicrobial (100 vs 15%, p<0.001) and complicated by bacteremia (50 vs 7%, p=0.011). A source of intraabdominal infection should be sought when Aeromonas peritonitis occurs in a patient who has no history of liver cirrhosis or who has a polymicrobial result of ascites culture.