Metformin-associated lactate acidosis is rare but serious and characterized by metabolic acidosis and elevated lactate. We describe a single-institution experience of four cases in one year. Despite pH levels of 6.85 to 7.12 and lactate levels of 11-28 mmol/l three of the patients survived. Two of the patients had normal kidney function previous to hospitalization. Treatment includes fluid replacement, IV sodium bicarbonate and haemodialysis.