When all of the macroscopic and microscopic features of Crohn's disease and ulcerative colitis are present, the correct diagnosis is usually made without difficulty. When some of the changes are absent, the accuracy of diagnosis is reduced. This review has outlined those diseases which feature some of these pathological changes and may masquerade as idiopathic chronic inflammatory bowel disease. Some of the pathological mimics are iatrogenic while other common diseases, such as bacterial infection, ischaemia, and diverticulosis may produce confusing histological appearances. The picture is complicated by the fact that many of these pathological imitators may themselves cause or predispose to chronic inflammatory bowel disease, or may complicate chronic inflammatory bowel disease. For example, drugs and infectious agents are recognisable causes of relapse in ulcerative colitis; Crohn's disease may cause diverticulitis in patients with diverticulosis; and lymphoma may complicate ulcerative colitis. It behooves all practising histopathologists to recognise these mimics of ulcerative colitis and Crohn's disease to ensure appropriate management for patients with inflammatory pathology of the intestines.