Recently, concern has been expressed about the hazards of lactic acidosis following the use of intravascular iodinated contrast agents in patients taking metformin. In response the Royal College of Radiologists have issued guidelines for the management of these patients. We have reviewed the reported cases of lactic acidosis and identified that in all cases underlying renal impairment existed. To examine this further we reviewed the notes of 33 in-patients receiving metformin who underwent contrast angiography in our hospital. Twenty-nine patients had a normal serum creatinine prior to the procedure and none had a rise following angiography. Four patients had an abnormal serum creatinine prior to angiography, all four patients showed significant deterioration and all four patients died, two from unrelated causes and two from acute renal failure and acidosis. These data strongly highlight the hazards of intravascular contrast radiology in diabetic patients with pre-existing renal impairment. We have failed to find evidence in support of the Royal College of Radiologists recommendation; instead we recommend that in those patients taking metformin with evidence of renal impairment metformin should be stopped and diabetic control obtained using alternative therapy before proceeding with angiography. Patients with normal renal function taking metformin are not at risk of lactic acidosis following the use of iodinated contrast agents for angiography.