OBJECTIVES: Patients with irritable bowel syndrome (IBS) report lower health-related quality of life (QoL) as compared to healthy controls. The aims of this analysis were to describe which IBS symptoms were rated on a daily diary as most distressing/severe by IBS women, and determine which IBS symptoms were most predictive of lower QoL and have the greatest impact on daily life. METHODS: This report is a secondary analysis of prospective and retrospective symptom severity and impact data, collected on 242 women with IBS, aged 18-48, who were studied between 1997 and 2004. RESULTS: On the daily diary, intestinal gas was the most frequent IBS symptom with subjects reporting at least minimal intestinal gas on 74% of days and moderate or worse severity on 27% of days. Abdominal pain occurred at least minimally on 62% of days. Diarrhea was the least common. Across women, abdominal pain was most strongly related to life impact variables and QoL, followed by intestinal gas and bloating. Analysis of day-to-day variation within women showed that abdominal pain was most strongly correlated with daily life impact variables and constipation had the weakest correlation. While diarrhea had a lower correlation with life impact, this was due to the low prevalence of diarrhea. When it occurs, diarrhea has a large impact. Partial correlation analysis showed that the impact of diarrhea is independent of abdominal pain. CONCLUSION: Abdominal pain is the most disruptive IBS symptom. Diarrhea also has an independent and significant impact when it occurs, especially in those with diarrhea-predominant IBS.