The involement of diverticula by granulomatous colitis may cause an increased incidence of diverticulitis. Of 21 patients with Crohn's disease and associated diverticulosis who underwent resection, sigmoid diverticulitis was pathologically confirmed in 10 (48%). The clinical recognition of the coexistence of the two diseases is often difficult. The radiological signs of peridiverticulitis complicating granulomatous colitis usually show clear evidence of the underlying pathological changes. They include localized diverticular performation, perhaps with multiple communications via a paracolonic sinus tract, mass pressure from the paracolicabscess, and occasionally some degree of communication with deep fissuring ulcers of Crohn's disease. Because diverticula breach the colonic wall, histological analysis confirm that their involvement by the transmural process of granulomatous colitis predisposes to peridiverticulitis and/or abscess formation.