Implanted cardioverter defibrillator therapy has been shown to be associated with a significant reduction in the risk of sudden cardiac death (SCD) in patients with ischemic left ventricular dysfunction. However, data on the relation between renal function and SCD in this population are limited, and the effect of renal dysfunction on the implanted cardioverter defibrillator benefit has not been determined. We performed a retrospective analysis of the outcome associated with renal dysfunction, as determined by the estimated glomerular filtration rate (eGFR), in patients enrolled in the Multicenter Automatic Defibrillator Implantation Trial-II. Multivariate analysis in conventionally treated patients showed that for each 10-U reduction in eGFR, the risk of all-cause mortality and SCD increased by 16% (p = 0.005) and 17% (p = 0.03), respectively. Defibrillator therapy was associated with a survival benefit in each eGFR category of > or = 35 ml/min/1.73 m2 (overall risk reduction for all-cause mortality 32%, p = 0.01 and for SCD 66%, p < 0.001). However, no implanted cardioverter defibrillator benefit was shown among patients with an eGFR < 35 ml/min/1.73 m2 (all-cause mortality hazard ratio 1.09, p = 0.84; SCD hazard ratio 0.95, p = 0.95). In conclusion, in patients with high-risk cardiac disease enrolled in the Multicenter Automatic Defibrillator Implantation Trial-II, a significant increase was found in the risk of SCD with declining renal function. Defibrillator therapy was associated with a significant survival benefit among the study patients with mild to moderate or no renal disease, but no benefit was shown among patients with more advanced renal dysfunction.