BACKGROUND: Pneumococcal peritonitis is uncommon and poorly understood.METHODS: As part of a five-year study (2000 to 2004) of invasive pneumococcal disease (IPD) in Alberta, all cases of peritonitis due to Streptococcus pneumoniae were reviewed and compared with all other cases of IPD.RESULTS: Twenty-three of 1768 (1.3%) IPD patients were found to have peritonitis. Patients with peritonitis were more likely to have cirrhosis, hepatitis C, alcoholism and HIV/AIDS, than the remainder of the patients with IPD. The all-cause mortality did not differ between the two groups. Peritonitis was classified as primary in nine (39%) patients, secondary in 12 (52%) patients, and genitourinary in females, specifically, in two (9%) patients. Pneumococcal serotypes causing peritonitis were under-represented in current vaccines – 17% among peritonitis patients versus 53% for the remainder of IPD patients for the 7-valent pneumococcal conjugate vaccine, and 56% versus 86% for the 23-valent pneumococcal polysaccharide vaccine.CONCLUSIONS: Peritonitis represents a small subset of patients with IPD, but one that is likely to grow in importance given the increase in the number of patients with hepatitis C and HIV, and the reduced coverage of peritonitis serotypes in currently available vaccines.