We examined symptom frequency, duration, and severity, as well as episode patterns, in 122 adult patients with irritable bowel syndrome in a 12-week study conducted in the United States, the United Kingdom, and The Netherlands. Patients used an interactive telephone data entry system daily to report symptoms. Data from 59 of the patients meeting inclusion criteria are presented, the remainder having been excluded for failing to complete at least 70 days of symptom reporting. The majority of patients experienced at least one symptom on over 50% of the reported days; however, individual symptoms were reported on less than 50% of the days, indicating that symptoms sometimes occurred sequentially rather than always simultaneously. On average, patients reported pain/discomfort on 33% of days, bloating on 28% of the days, altered stool form or stool passage on 25% and 18% of the days, respectively, and mucus on 7% of the days. The duration of symptoms was relatively short, with pain/discomfort and bloating lasting the longest, an average of five days each per episode. All symptoms but one (mucus) were moderately severe on the majority of reported days. Patients experienced an "episode" (defined as a period of days with symptoms bounded by one or more symptom-free days) on an average of 12.4 times during the study, but the duration of these episodes varied greatly among patients. These results further establish the chronic nature of irritable bowel syndrome and the burden that this condition imposes on patients.