Tumour necrosis factor-α expression may be increased in segmental colitis associated with diverticulosis.To assess tumour necrosis factor-α expression in segmental colitis associated with diverticulosis in relation with the severity of the endoscopic damage.21 patients affected by segmental colitis associated with diverticulosis were studied (15 M, 6 F, mean age 58.87 years, range 43–85 years). Segmental colitis associated with diverticulosis was graduated as mild-moderate (patterns A and C) and severe (patterns B and D). Ten patients with moderate-to-severe ulcerative colitis, 10 patients with moderate-to-severe Crohn's disease, and 10 patients with irritable bowel syndrome served as control groups.Tumour necrosis factor-α expression was significantly higher in segmental colitis associated with diverticulosis B (42.7%) and segmental colitis associated with diverticulosis D (40%) than in segmental colitis associated with diverticulosis A (19.1%) and segmental colitis associated with diverticulosis C (21.1%).Tumour necrosis factor-α expression was lower in segmental colitis associated with diverticulosis A and C than in ulcerative colitis and Crohn's disease, whilst no different tumour necrosis factor-α expression was found between segmental colitis associated with diverticulosis B and D and both ulcerative colitis and Crohn's disease.Finally, tumour necrosis factor-α expression was significantly lower in irritable bowel syndrome (8%±4) than in every type of segmental colitis associated with diverticulosis.Tumour necrosis factor-α expression in segmental colitis associated with diverticulosis seems to be related to the severity of the endoscopic damage. This behaviour, similar to that of the inflammatory bowel diseases (IBD), confirms that this disease should be considered as a subtype of IBD.