AIMS: Little is known about the mortality for patients with infective endocarditis (IE) on a nationwide scale, and previous studies have been conducted in selected cohorts from tertiary centers. We aimed to investigate temporal trends in mortality using nationwide Danish registries. METHODS AND RESULTS: We identified patients with first-time IE between 1999-2018, and they were grouped by calendar periods (1999-2003, 2004-2008, 2009-2013, 2014-2018). One-year mortality was estimated using Kaplan-Meier estimates. For calendar periods, odds ratios (ORs) and hazard ratios (HRs) were computed using multivariable adjusted logistic regression and Cox proportional Hazards analyses for in-hospital and one-year mortality, respectively. We identified 8804 patients with IE. Age and proportions of men were: 66.7 (25th-75th percentile: 53.4-76.7) years and 59.9% in 1999-2003 and 72.8 (25th-75th percentile: 63.4-80.3) and 65.8% in 2014-2018. In-hospital mortality was 1999-2003: 24.5%, 2004-2008: 22.8%, 2009-2013: 18.8%, and 2014-2018: 18.3%. Relative to 1999-2003, adjusted likelihoods of in-hospital mortality were: OR = 0.81 (95% CI: 0.69-0.96) in 2004-2008, OR = 0.59 (95% CI: 0.50-0.69) in 2009-2013, and OR = 0.51 (95% CI: 0.43-0.60) in 2014-2018. By calendar periods, crude risks of one-year mortality were: 34.4% (95% CI: 32.0-36.8%), 33.5% (95% CI: 31.5-35.6%), 32.1% (95% CI: 30.2-34.0%), and 33.1% (95% CI: 31.3-34.8%). Relative to 1999-2003, adjusted rates of one-year mortality were: HR = 0.88 (95% CI 0.79-0.99) in 2004-2008, HR = 0.76 (95% CI: 0.68-0.86) in 2009-2013, and HR = 0.72 (95% CI: 0.64-0.81) in 2014-2018. CONCLUSION: In this nationwide study of patients with first-time IE between 1999-2018, both short- and long-term survival has improved over time when accounting for changes in patient characteristics. ONE-SENTENCE SUMMARY: When accounting for patient characteristics, both short- and long-term mortality have improved in patients with first-time infective endocarditis.