Fifty-eight patients with uncomplicated diverticular disease of the colon took bran crispbread, ispaghula drink, and placebo for four months each in a randomised, cross-over, double-blind controlled trial. Assessments were made subjectively, using a monthly self-administered questionnaire, and objectively, by examining a seven-day stool collection at the end of each treatment period. In terms of a pain score, lower bowel symptom score (the pain score and sensation of incomplete emptying, straining, stool consistency, flatus, and aperients taken), and total symptom score (belching, nausea, vomiting, dyspepsia, and abdominal distension) fibre supplementation conferred no benefit. Symptoms of constipation, however, when assessed alone, were significantly relieved. Both fibre regimens produced the expected changes in stool weight, consistency, and frequency. It is concluded that dietary fibre supplements in the commonly used doses do no more than relieve constipation. Perhaps the impression that fibre helps diverticular disease is simply a manifestation of Western civilisation's obsession with the need for regular frequent defecation.