Dyspepsia and irritable bowel syndrome (IBS) share aetiopathogenic factors, and may therefore be part of a single disorder. This study was intended to determine their prevalence in the general population, and the degree of overlap between these two digestive disorders. Descriptive study. A sample of 264 subjects chosen randomly from the population census of a city in Spain, and considered representative of the general population in this city, was surveyed by questionnaire. The prevalence of dyspepsia was 23.9%, and that of IBS was 13.6%. Of the subjects with dyspepsia, 31.6% had IBS, and of the subjects with IBS, 55.6% reported symptoms of dyspepsia. The prevalence of IBS was higher among subjects with dyspepsia (31.7%) than among those who reported no symptoms of dyspepsia (7.9%; P < 0.05). Moreover, the prevalence of IBS was similar in three subgroups identified according to the type of dyspepsia described (ulcer-like, reflux-like or dysmotility-like). When we compared subjects with both dyspepsia and IBS and those with dyspepsia alone, we found no significant differences in clinical characteristics except for abdominal pain and fear of cancer, which were more frequent in the former. Of the entire sample, 27.7% of the subjects sought medical attention for IBS and 17% missed work because of IBS. Our findings suggest that functional dyspepsia and IBS are two manifestations of a single, more extensive digestive system disorder.