Spontaneous bacterial peritonitis (SBP) is a complication of liver cirrhosis with high mortality and low survival rates. The incidence of SBP is reported to range from 11-35% in patients with ascites requiring hospitalization. Under clinical experience, the incidence of SBP in Finland seems to be lower than reported elsewhere. Alcohol is the dominant etiologic factor of liver cirrhosis in Finland (90%), which might be a factor affecting the incidence of SBP. The aim of this study is to measure the incidence of SBP in Finland. We included consecutive patients who underwent diagnostic paracentesis for ascites in Tampere University Hospital during 2/1994 - 12/1998 and 1/2005 - 3/2007. Spontaneous bacterial peritonitis was diagnosed when the ascitic fluid contained over 250 polymorphonuclear cells / mm^3 regardless of culture and with no evidence of intra-abdominal source of infection e.g. an abscess or a perforation.