Spontaneous bacterial peritonitis (SBP) is considered a bacterial infection of ascitic fluid without any intraabdominal, surgically treatable source of infection. Multiple variants of this infection with a different clinical setting and outcome have been described during the past decade. Bacterial translocation from the gut to mesenteric lymph nodes, depressed activity of the reticuloendothelial phagocytic system and decreased antimicrobial capacity of ascitic fluid seem to be the main steps in the pathogenesis of ascitic fluid infection. Diagnosis of ascitic fluid infection is based on clinical suspicion and analysis of ascitic fluid, especially white cell count and culture in blood culture bottles. A low threshold for performing an abdominal paracentesis is the key for an early diagnosis and treatment. A third-generation cephalosporin is the treatment of choice, achieving a cure rate higher than 80%. Nonazotemic patients with nonadvanced, uncomplicated SBP may be treated with oral ofloxacin. Prophylactic selective intestinal decontamination with oral norfloxacin is extremely useful in preventing SBP in patients that are at high risk for developing SBP, such as hospitalized cirrhotic patients with gastrointestinal hemorrhage or low ascitic fluid total protein. Primary or secondary long-term prophylaxis of SBP also decreases the incidence of SBP, but these patients should be carefully observed for detecting possible infections caused by quinolone-resistant organisms. Since long-term prognosis of SBP patients is poor, survivors should be considered for liver transplantation.