It is recognized that inflammatory bowel diseases predispose to colorectal adenocarcinoma. Early detection of precursor lesions and subsequent treatment may prevent cancer development and this is possible with colonoscopy and biopsy. Inflammatory bowel disease-associated precursor lesions (dysplasia = intraepithelial neoplasia) must be distinguished from sporadic adenomas, occurring in non-colitic mucosa. Macroscopic lesions suspected of harbouring precursor lesions include irregular 'polypoid or elevated' lesions, which are usually broad-based and 'flat' lesions. Flat lesions are more common than elevated lesions and they are usually smaller. Chromoendoscopy increases the detection rate substantially as it allows targeted biopsies from suspicious lesions that increase the diagnostic yield of dysplasia. Ultimately, the combination of chromoendoscopy, or more advanced endoscopic techniques, and targeted biopsies may become the standard approach, rather than random biopsy sampling.