DANISH (The Danish Study to Assess the Efficacy of Implantable Cardioverter Defibrillators ICDs in Patients With Nonischemic Systolic Heart Failure on Mortality) found that primary-prevention ICD implantation was not associated with an overall survival benefit in patients with nonischemic systolic heart failure during a median follow-up of 5.6 years, although there was a beneficial effect on all-cause mortality in patients ≤70 years. This study presents an additional 4 years of follow-up data from DANISH. In DANISH, 556 patients with nonischemic systolic heart failure were randomized to receive an ICD and 560 to receive usual clinical care and followed until June 30, 2016. In this long-term follow-up study, patients were followed until May 18, 2020. Analyses were conducted for the overall population and according to age (≤70 and >70 years). During a median follow-up of 9.5 years (25th-75th percentile, 7.9-10.9 years), 208/556 patients (37%) in the ICD group and 226/560 patients (40%) in the control group died. Compared with the control group, the ICD group did not have significantly lower all-cause mortality (hazard ratio HR 0.89, 95% CI, 0.74-1.08; = 0.24). In patients ≤70 years (n = 829), all-cause mortality was lower in the ICD group than the control group (117/389 30% versus 158/440 36%; HR, 0.78 95% CI, 0.61-0.99; = 0.04), whereas in patients >70 years (n = 287), all-cause mortality was not significantly different between the ICD and control group (91/167 54% versus 68/120 57%; HR, 0.92 95% CI, 0.67-1.28; = 0.75). Cardiovascular death showed similar trends (overall, 147/556 26% versus 164/560 29%; HR, 0.87 95% CI, 0.70-1.09; = 0.20; ≤70 years, 87/389 22% versus 122/440 28%; HR, 0.75 95% CI, 0.57-0.98; = 0.04; >70 years, 60/167 36% versus 42/120 35%; HR, 0.97 95% CI, 0.65-1.45; = 0.91). The ICD group had a significantly lower incidence of sudden cardiovascular death in the overall population (35/556 6% versus 57/560 10%; HR, 0.60 95% CI, 0.40-0.92; = 0.02) and in patients ≤70 years (19/389 5% versus 49/440 11%; HR, 0.42 95% CI, 0.24-0.71; = 0.0008), but not in patients >70 years (16/167 10% versus 8/120 7%; HR, 1.34 95% CI, 0.56-3.19; = 0.39). During a median follow-up of 9.5 years, ICD implantation did not provide an overall survival benefit in patients with nonischemic systolic heart failure. In patients ≤70 years, ICD implantation was associated with a lower incidence of all-cause mortality, cardiovascular death, and sudden cardiovascular death. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT00542945.