A prospective, one-month diary study was conducted with 23 adult irritable bowel syndrome (IBS) patients in order to determine the relationship between IBS and the quality of sleep. Subjects were screened through history and diagnostic studies. Accepted patients then completed a daily diary of IBS symptoms and sleep quality. At baseline, most subjects (74%) characterized themselves as "poor sleepers." Using pooled time series analysis, the study found a significant correlation between morning IBS symptoms and the quality of the prior night's sleep (P < 0.001), a finding not previously reported in the literature. A less strong but still significant correlation (P < 0.05) was found between end of day IBS symptoms and the quality of sleep during the prior evening. Morning IBS symptoms seem to rise or fall in close association with the prior night's quality of sleep. The study supports the hypothesis that IBS symptoms are related to a disturbance in sleep.