Mycophenolate mofetil (MMF) is now the preferred antimetabolite for post-transplant immunosuppression [1]. Although leucopenia and diarrhoea are the main side effects, there are case reports of a malabsorption syndrome caused by MMF [2]. Oxalosis, either primary or secondary, is a wellrecognised cause for renal failure. Secondary hyperoxaluria is caused by increased intestinal oxalate absorption and can be aggravated by excessive dietary oxalate intake. Particular gastro-intestinal disorders such as short bowel syndrome, chronic inflammatory bowel disease and fat malabsorption syndromes, e.g. chronic pancreatitis, are known to increase the risk of secondary hyperoxaluria [3]. Oxalosis causing renal allograft failure has also been reported [4,5]. To our knowledge, MMF has not previously been implicated in the development of secondary hyperoxaluria and acute renal failure in kidney or kidney–pancreas transplant patients. We report a patient with prolonged MMF-associated diarrhoea who presented with acute renal failure caused by oxalosis.