Aims/hypothesis Fenofibrate caused an acute, sustained plasma creatinine increase in the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) and Action to Control Cardiovascular Risk in Diabetes (ACCORD) studies. We assessed fenofibrate's renal effects overall and in a FIELD washout sub-study. Methods Type 2 diabetic patients (n=9,795) aged 50 to 75 years were randomly assigned to fenofibrate (n=4,895) or placebo (n=4,900) for 5 years, after 6 weeks fenofibrate run-in. Albuminuria (urinary albumin/creatinine ratio measured at baseline, year 2 and close-out) and estimated GFR, measured four to six monthly according to the Modification of Diet in Renal Disease Study, were pre-specified endpoints. Plasma creatinine was re-measured 8 weeks after treatment cessation at close-out (washout sub-study, n=661). Analysis was by intention-to-treat. Results During fenofibrate run-in, plasma creatinine increased by 10.0 μmol/l (p<0.001), but quickly reversed on placebo assignment. It remained higher on fenofibrate than on placebo, but the chronic rise was slower (1.62 vs 1.89 μmol/l annually, p=0.01), with less estimated GFR loss (1.19 vs 2.03 ml min −1 1.73 m −2 annually, p<0.001). After washout, estimated GFR had fallen less from baseline on fenofibrate (1.9 ml min −1 1.73 m −2 , p=0.065) than on placebo (6.9 ml min −1 1.73 m −2 , p<0.001), sparing 5.0 ml min