The influence of colonic diverticula on symptomatology and prognosis was investigated in 69 patients with irritable bowel syndrome. Roentgenograms at the time of diagnosis were blindly correlated to patient complaints and to result of follow-up 5 to 7 yr after the irritable bowel syndrome had been diagnosed. Patient complaints were not related to the presence or extent of diverticulosis. Half the patients had unchanged or aggravated symptoms at follow-up irrespective of diverticulosis. Accordingly, the presence of colonic diverticula did not change the natural history of the irritable bowel syndrome.