Patterns of illness or disability-related work absence six months before and six months after a diagnosis of irritable bowel syndrome (IBS) were assessed from medical claims and absenteeism databases and were compared with a sample of patients with no gastrointestinal (GI) disorders. The records of 630 patients with IBS were compared with those of 1,260 persons without GI conditions. Mean monthly IBS-related absences increased by 69% (from 0.96 to 1.62 days) from the beginning of the six-month period before diagnosis to the month of diagnosis. With multivariate regression analysis, the incremental effect of an IBS diagnosis on six-month absenteeism was estimated to be 3.27 absences greater for persons with IBS.