Diverticular disease of the right colon is not common, especially in western countries. It occurs in two different clinical forms, known as the "usual" and "hidden" variants. The diagnosis is not always easy, especially in the latter variant, because sometimes barium enema and CT scan are unable to distinguish this form from cancer. The final diagnosis is only intraoperative. In our experience, from 1994 to 2004, we observed 4 cases of complicated right-sided diverticulitis. Three of these patients had symptoms mimicking acute appendicitis, such as fever and abdominal pain. Only 2 of them underwent surgical treatment consisting of a right standard hemicolectomy. The 4th patient had no inflammatory symptoms, but had a history of right-sided abdominal pain and diarrhoea. Laboratory data showed only hypochromic anaemia. Barium enema and CT scan highlighted a vegetating mass in the ascending colon causing irregular severe stenosis of the lumen and hyperdensity of mesocolic fatty tissue. Surgical treatment consisted in a right hemicolectomy. Macroscopically, the mass involved the caecum and ascending colon. Enlarged lymph-nodes were present in the thickness of the mesocolon, but not in other districts. Histological examination revealed diffuse diverticular disease complicated by perforation of many diverticula into the mesocolon.