A 52-year-old woman with a medical history of diabetes mellitus type 2, chronic alcoholism and liver function disorders was hospitalized because of complaints of haematemesis, abdominal complaints and dyspnoea. This was due to a severe lactic acidosis caused by acute alcohol intoxication and the use of metformin. With bicarbonate infusion and haemofiltration, the lactic acidosis disappeared, but she developed a distributive shock with multiple organ failure and died 23 days after admission. Lactic acidosis is a rare but serious adverse effect of metformin. Almost all patients described had contraindications to the drug, like renal failure, liver disease, alcohol abuse, and intercurrent conditions causing hypoxia or ischaemia. It is important to be aware of the circumstances in which metformin should not be prescribed.