A study is reported in which the prevalence of symptomless diverticular disease of the colon is related to the consumption of dietary fibre in vegetarians and non-vegetarians. Vegetarians had a significantly higher mean fibre intake (41·5 g/day) than non-vegetarians (21·4 g/day). Diverticular disease was commoner in non-vegetarians (33%) than in vegetarians (12%). Comparison of subjects with and without diverticular disease in the vegetarian and non-vegetarian groups provided some further evidence that a low intake of cereal fibre is associated with the presence of diverticular disease.