Metformin, an anti-hyperglycaemic drug, reduces mortality in obese patients with a non-insulin-dependent diabetes mellitus type II (United Kingdom Prospective Diabetes Study) and is therefore recommended as the first line therapy. A metformin-associated lactic acidosis due to accumulation or intoxication is a rare but severe complication with a mortality rate of up to 50%. The main clinical symptoms are unspecific and the patient may present with acute abdominal pain and reduced consciousness. This can easily be misinterpreted and may lead to a wrong diagnosis. Only a thorough clinical examination and exact analysis of laboratory values in combination with the medical history and chronic medication will allow a correct diagnosis. We report a case of a 79-year-old female patient whose clinical symptoms were initially interpreted as an acute intestinal ischemia. A progressively deteriorating haemodynamic state led to an exploratory laparotomy. Postoperatively, the correct diagnosis of a metformin-associated lactic acidosis due to acute renal failure was made. In the course of the ICU stay the condition improved after bicarbonate haemodialysis and the patient was discharged 11 days after admission.