The importance of colorectal biopsies in the diagnosis and management of inflammatory bowel disease (IBD) is reviewed and the histologic criteria for identifying the different types of colitis are outlined. While most of the histopathologic features of the various forms of colitis are characteristic, none is pathognomonic. Accordingly, emphasis is placed on considering all clinical and investigational data in evaluating histopathologic changes found in colorectal mucosal biopsies.