One hundred and twenty consecutive patients with liver cirrhosis and ascites were prospectively studied in order to analyze the frequency, clinical and bacteriological features, recurrence, and prognosis of spontaneous bacterial peritonitis (SBP). Two variants of SBP were defined: culture positive SBP and culture negative neutrocytic ascites (CNNA). During a follow-up of 6 +/- 2 months, thirty three episodes in 23 patients were identified. Nineteen episodes had ascites positive cultures (58%). The total mortality rate associated with SBP was 39%. (47% for culture positive form and 29% for CNNA). Seven of 15 cirrhotics who had recovered from a first episode of SBP (46%) had 10 recurrences. Mortality associated with SBP recurrence was 50%. Six-month survival probability was 65% in patients with sterile ascites and 33% in SPB (p < 0.05). Impairment of liver function was present in 23 episodes (70%) but abdominal complaints occurred only in one/third and 4 (12%) were asymptomatic. E coli was the most frequent agent involved in culture positive SBP. We confirm that SBP is a frequent, recurrent and severe complication of ascites in cirrhotics. Episodes of SBP without abdominal symptoms or with a silent course are not infrequent. Then, SBP recognition requires ample use of diagnostic paracentesis.