OBJECTIVES: Heavy alcohol intake may exacerbate gastrointestinal (GI) symptoms in adults with irritable bowel syndrome (IBS); however, the role of alcohol in IBS is unclear. We investigated prospective associations between daily patterns of alcohol intake and next day's GI symptoms using daily diaries. METHODS: In an observational study of women aged 18-48 years with IBS and healthy controls, participants recorded daily GI symptoms, alcohol intake, caffeine intake, and cigarette smoking for ≈ 1 month. GI symptoms included abdominal pain, abdominal bloating, intestinal gas, diarrhea, constipation, nausea, stomach pain, heartburn, and indigestion. Binge drinking was defined as 4+ alcohol-containing drinks/day. RESULTS: Patterns of alcohol intake did not differ between IBS patients and controls. Although patterns of drinking were associated with GI symptoms among women with IBS, this was not the case with the healthy controls. The strongest associations for IBS patients were between binge drinking and the next day's GI symptoms (e.g., diarrhea, P=0.006; nausea, P=0.01; stomach pain, P=0.009; and indigestion, P=0.004), whereas moderate and light drinking either were not associated or weakly associated with GI symptoms. Associations between alcohol intake and GI symptoms were stronger for women with IBS-diarrhea than for IBS-constipation or IBS-mixed. Effects of binge drinking on GI symptoms were strongest when comparing between individuals (rather than within individuals). CONCLUSIONS: Our findings indicate that IBS symptoms differ according to the pattern of alcohol intake among IBS patients, suggesting that the pattern of drinking may in part explain the inconsistent findings between alcohol and IBS symptoms.