Recommendations for prophylactic implantable cardioverter defibrillator (ICD) implantation in asymptomatic heart failure patients with a reduced left ventricular ejection fraction (LVEF) differ between guidelines. Evidence on the risk of appropriate device therapy (ADT) and death in New York Heart Association (NYHA) class I patients is scarce. Aim of this study is to evaluate ADT and mortality in NYHA-I primary prevention ICD patients with a LVEF ≤35%. A retrospective cohort was studied, including 572 patients with LVEF ≤35% who received a prophylactic ICD with or without resynchronization therapy (CRT-D). To evaluate the incidence of ADT and mortality, NYHA-I was compared with NYHA-II-III using Cox regression analysis. During a follow-up of 4.1 ± 2.4 years, 33% of the NYHA-I patients received ADT compared with 20% of the NYHA-II-III patients (hazard ratio 1.5, 95% confidence interval 1.04 to 2.31, p = 0.03). No differences in mortality were observed (hazard ratio 0.70, 95% confidence interval 0.49 to 1.07, p = 0.10). Additional analyses showed no difference in time to ADT excluding CRT patients (ICD-NYHA-I patients vs ICD-NYHA-II-III patients, p = 0.17) and comparing ischemic and nonischemic cardiomyopathy NYHA-I patients (p = 0.13). Multivariable Cox regression analyses showed that NYHA class was the strongest independent predictor of ADT. In conclusion, primary prevention NYHA-I ICD patients showed a higher incidence of ADT compared with NYHA-II-III ICD patients. These results strongly suggest that primary prevention NYHA-I patients with a LVEF ≤35% are likely to benefit from ICD therapy and should not be excluded from a potentially life-saving therapy.