The authors describe rare complications of advanced colorectal carcinoma--duodenocolic fistulae, which unless removed by surgery, soon kill the patient. The authors draw attention to the clinical picture where rapidly developing dehydration, anaemia and general cachexia predominate. After short-term preoperative preparation (adequate parenteral nutrition, transfusion of blood and blood derivatives, antibiotics etc.), the authors recommend, consistent with data in the literature, radical surgery, i.e. right-sided pancreatectomy with right-sided hemicolectomy or at least right-sided hemicolectomy with excision of the fistula on the duodenum and intense postoperative care. Bypass operations are recommended as palliative operations where radical operation is not possible for some reason. A malignant duodenocolic fistula as a complication of an advanced malignant disease in a very exhausted patient may fail even after a radical, technically perfect operation and intense preoperative and postoperative care.