Over many decades the surgical treatment of gastrointestinal tumours was limited to cases of manifest malignancy and was performed with curative or palliative intent. Molecular diagnostics have now led to an optimised characterisation of different sporadic and hereditary tumour entities. Furthermore, a number of diseases which are an obligatory precancerosis or which carry a very high risk of cancer in their long courses have now been identified. Parallel to these developments, a dramatic reduction of morbidity has been achieved in major abdominal surgery due to more subtle and blood-sparing surgical techniques and mortality has been reduced to a minimum even in the most major procedures. This combination nowadays safely allows preventive or preventive extended surgical measures in cases where interventional therapy cannot be adequately employed.