SUMMARY Background: A genetic contribution has been proposed for irritable bowel syndrome (IBS) and gastro-oesophageal reflux disease (GERD), but is controversial. No twin data exist for dyspepsia. Aim: To determine the relative contribution of genetic factors in GERD, dyspepsia (upper abdominal pain) and IBS. Methods: A total of 986 twin pairs (from initial mail-out response 51%). Both members completed validated symptom and psychological questionnaires; 481 monozygotic pairs [mean (s.d.) age 53 ± 5.8 years] and 505 dizygotic pairs (mean age 54 ± 5.6 years). Results: Prevalence of IBS, dyspepsia and GERD was 12%, 10% and 20%, respectively. Polychoric correlation for monozygotic twins for IBS (0.47) and GERD (0.44) were both substantially larger than those for dizygotic twins (0.17 and )0.37, respectively). Polychoric correlation was slightly lower in monozygotic than dizygotic twins for dyspepsia. Genetic modelling confirmed the independent additive genetic effects in GERD and IBS but not dyspepsia. Estimates of genetic variance were 22% for IBS, 13% for GERD and 0% for dyspepsia, but adjusting for anxiety and depression removed the statistical significance for IBS and GERD. Conclusions: There is a genetic contribution to GERD and IBS but not dyspepsia; this may be mediated by the hereditability of anxiety and depression.