Risk of development of some gastrointestinal tract cancers (colorectal cancer, pancreas cancer and liver cancer) is higher in type II diabetics. Another important risk factor is obesity (for gall bladder cancer in women and in men also for stomach and esophageal cancer). Pathogenetic factors have been explored especially in colorectal cancer (diet, hyperinsulinaemia, metabolic receptors activation, absence of physical activity). Our Czech study also proved up to 4 times increased risk of colorectal cancer in diabetics and, in accordance with literature, probable influence of persistent diabetes on tumour development. Type II diabetes mellitus should be considered as a risk factor especially for colorectal cancer, liver cancer, and pancreas cancer. In type I diabetics no risk of gastrointestinal tract cancers was proved.

        Key words: Diabetes mellitus - Gastrointestinal tract tumours - Colorectal cancer - Metabolic syndrome - Pancreas cancers - Obesity - Diet factors