Background: Patients with ischemic left ventricular dysfunction have a high risk of sudden cardiac death (SCD). It is, however, unclear if the risk and risk factors of SCD in these patients is modulated by the coexistence of mild chronic renal insufficiency. Methods: We performed a post-hoc analysis of the outcome associated with mild renal dysfunction, as defined by an estimated glomerular filtration rate (eGFR) of <75 ml/min/1.73 m<sup>2</sup> in patients allocated to the conventional medical therapy arm of the Multicenter Automatic Defibrillator Implantation Trial-II. Results: In multivariable analysis, renal dysfunction was independently associated with significant increased risks for all-cause mortality (hazard ratio [HR] = 1.86; 95% CI 1.13–3.05) and SCD (HR = 2.00; 95% CI 1.01–4.02), but not non-SCD, compared to patients without renal dysfunction. Independent predictors of SCD in patients with renal dysfunction were: increased resting heart rate (HR = 2.40; 95% CI 1.50–3.86); low diastolic blood pressure (HR = 3.23; 95% CI 1.52–6.66), and a prolonged QRS duration (HR = 1.63; 95% CI 1.02–2.61). β-Blocker therapy was independently associated with a significant reduction in the risk of SCD in patients with an eGFR of <75 ml/min/1.73 m<sup>2</sup> (HR = 0.61; 95% CI 0.38–0.99). Conclusion: These findings suggest that renal dysfunction significantly increases the risk for SCD in patients with left ventricular dysfunction, and that β-blocker therapy reduces the risk of arrhythmic mortality in heart failure patients with coexisting renal insufficiency.