In the 1990s, there was anxiety about the risk of lactic acidosis if intravascular iodinated contrast media caused nephrotoxicity in non-insulin-dependent diabetic patients on metformin. Guidelines from the European Society of Urogenital Radiology (ESUR) published in 1999 indicated that metformin administration should be stopped from the time of contrast medium administration for 48 h and only restarted when serum creatinine had been shown to be normal ( Thomsen et al. 1999). Since 1999, new data on the risk of metformin-associated lactic acidosis have become available and clinical practice for prescribing metformin to diabetic patients with impaired renal function has changed.