Background: Chronic kidney disease (CKD) is associated with worse survival in patients with implantable cardiac defibrillators (ICDs). This study examined the association of outcomes with CKD in patients receiving an ICD for primary versus secondary prevention. Methods: The study included 696 patients who underwent ICD placement for clinical reasons (59% primary, 41% secondary prevention) at the University of Alabama at Birmingham between January 2002 and September 2007. CKD was defined as an estimated glomerular filtration rate < 60 ml/min/1.73 m2 but not on dialysis. Outcomes of interest included overall mortality and first appropriate ICD therapy (shocks or anti-tachycardia pacing). Results: After a follow-up of 50 ± 24 months, 213 patients died (31%) and 111 (16%) received appropriate ICD therapy. Patients with CKD had higher mortality than patients with no CKD in the primary (43% vs. 15%, p < 0.001) and secondary prevention (37% vs. 23%, p = 0.003) groups. Patients with CKD were at higher risk of receiving an appropriate ICD therapy than patients without CKD in the primary (p < 0.001) but not secondary prevention (p = 0.9) cohort. After adjusting for age, gender and multiple risk factors, CKD was independently associated with all-cause mortality and ICD therapy in the primary prevention group (HR 2.08 [1.34-3.23] and 3.53 [1.75-7.10], p = 0.001 and < 0.0001, respectively) but not in the secondary prevention group (HR 1.27 [0.81-2.00], and 0.63 [0.35-1.13], p = 0.3 and 0.2, respectively). Conclusions: CKD is independently associated with increased mortality and appropriate ICD therapy in patients undergoing ICD implantation for primary but not secondary prevention. © 2011 Elsevier Ireland Ltd.