Colorectal carcinoma is one of the most common tumour entities in Western countries. Colorectal carcinoma and type 2 diabetes mellitus share common risk factors. Recent epidemiological studies show an increased risk for colorectal carcinomas in patients with type 2 diabetes mellitus, even more pronounced at therapy with sulfonylureas or insulin. Moreover, a 3-fold risk increase for patients with insulin-dependent type 2 diabetes mellitus in comparison to the general population has been observed. The hyperinsulinaemia hypothesis is based on the premise that elevated plasma levels of insulin and free IGF-1 promote the proliferation of colon cells and lead to a survival benefit of transformed colon carcinoma cells. This is reflected by an altered tumour biology; in patients with type 2 diabetes, tumour progression is more rapid and tumour-associated mortality is increased. Colorectal carcinoma represents an entity that is well amenable to and can potentially be avoided by screening colonoscopy. Recommendations for colorectal carcinoma screening should employ the recent epidemiologic evidence. All patients with type 2 diabetes should be recommended to undergo colonoscopy before starting insulin therapy, and screening intervals should not exceed 5 years. This work provides a review of the evidence, and an algorithm is proposed for a modified screening in patients with type 2 diabetes.