A total of 89 patients with alcoholic cirrhosis and 40 healthy subjects were included in a study to assess the prevalence of intestinal bacterial overgrowth and to analyze its relationship with the severity of liver dysfunction, presence of ascites, and development of spontaneous bacterial peritonitis (SBP). Bacterial overgrowth was measured by means of a breath test after ingestion of glucose. Intestinal bacterial overgrowth was documented in 27 (30.3%) of the 89 patients with alcoholic cirrhosis and in none of the healthy subjects. The prevalence of intestinal bacterial overgrowth was significantly higher in cirrhotics with ascites (37.1%) than in those with no evidence of ascites (5.3%) and among patients with Pugh-Child class C (48.3%) than in patients with a class A (13.1%) or B (27%). Twelve (17.1%) of the 70 patients with ascites developed an episode of SBP. The prevalence of spontaneous bacterial peritonitis was significantly higher in patients who had intestinal bacterial overgrowth (30.7%) than in patients who did not (9.09%). We conclude that intestinal bacterial overgrowth occurs in approximately one third of patients with cirrhosis secondary to alcohol, particularly in patients with ascites and advanced liver dysfunction. Moreover, bacterial overgrowth may be a condition favoring infection of the ascitic fluid.