Irritable bowel syndrome (IBS), a chronic disorder that includes symptoms such as abdominal pain and altered bowel habits, affects up to 22% of people in Western populations. The causes of IBS are not well understood, but are believed to be multifactorial. Although stress is widely believed to be implicated, empirical evidence in support of this is lacking, perhaps because a typical between-participants analysis ignores individual differences and therefore may obscure any link. The present study used a within-person, lagged time-series approach to investigate the links between everyday stress and symptomatology in 31 IBS sufferers. Both everyday stress and symptomatology exhibited serial dependence for a statistically significant proportion of sufferers. Multiple regression analysis carried out on same-day and lagged relationships up to and including 4 days found that, for over half the participants, everyday stress and symptoms were related. The best regression model was one in which symptoms were a function of hassles and symptoms on the previous 2 days, and hassles on the same day, fitting the data for 67% of participants. This prospective study confirms other studies that have suggested stress is a significant factor in IBS, and concludes that stress management programs may be both useful and cost-effective in the treatment of IBS.