Abstract Aims Current treatment guidelines recommend implantable cardioverter-defibrillators (ICDs) in eligible patients with an estimated survival beyond 1 year. There is still an unmet need to identify patients who are unlikely to benefit from an ICD. We determined cause-specific 1-year mortality after ICD implantation and identified associated risk factors. Methods and results Using Danish nationwide registries (2000–2017), we identified 14 516 patients undergoing first-time ICD implantation for primary or secondary prevention. Risk factors associated with 1-year mortality were evaluated using multivariable logistic regression. The median age was 66 years, 81.3% were male, and 50.3% received an ICD for secondary prevention. The 1-year mortality rate was 4.8% (694/14 516). ICD recipients who died within 1 year were older and more comorbid compared to those who survived (72 vs. 66 years, P < 0.001). Risk factors associated with increased 1-year mortality included dialysis [odds ratio (OR): 3.26, confidence interval (CI): 2.37–4.49], chronic renal disease (OR: 2.14, CI: 1.66–2.76), cancer (OR: 1.51, CI: 1.15–1.99), age 70–79 years (OR: 1.65, CI: 1.36–2.01), and age ≥80 years (OR: 2.84, CI: 2.15–3.77). The 1-year mortality rates for the specific risk factors were: dialysis (13.8%), chronic renal disease (13.1%), cancer (8.5%), age 70–79 years (6.9%), and age ≥80 years (11.0%). Overall, the most common causes of mortality were related to cardiovascular diseases (62.5%), cancer (10.1%), and endocrine disorders (5.0%). However, the most common cause of death among patients with cancer was cancer-related (45.7%). Conclusion Among ICD recipients, mortality rates were low and could be indicative of relevant patient selection. Important risk factors of increased 1-year mortality included dialysis, chronic renal disease, cancer, and advanced age.