Leucopenia and diarrhoea are the main side effects observed after the use of mycophenolate mofetil (MMF) in renal-transplant patients. The mechanism of diarrhoea remains unknown. We report on four cases presenting with severe diarrhoea, which appeared, respectively, at 4, 10, 24, and 66 months after MMF therapy had been started. All patients presented with weight loss and biological signs of malabsorption syndrome. Oesophago-gastroduodenoscopy revealed duodenal villous atrophy, which was confirmed by pathology examination. Anti-endomysium antibodies were negative. In all patients, diarrhoea disappeared within 1 month of MMF withdrawal without a gluten-free diet. A control oesophago-gastroduodenoscopy was performed in one patient 6 months later and was considered normal. None of the patients showed evidence of cytomegalovirus in enterocytes or cytomegalovirus-positive viraemia. In conclusion, villous atrophy induced by MMF might be one of the mechanisms of diarrhoea. It is mandatory to differentiate coeliac disease from MMF-induced villous atrophy because, in the latter case, a gluten-free diet is not required.