Abstract Background/Introduction Sudden cardiac death in the young (SCDY) constitutes an important public health problem and many years lost to society. Several initiatives have been implemented to reduce the rate of SCDY, e.g. improved resuscitation. Declining rates of overall and cardiovascular disease mortality have been well-documented; however, reliable information on the contemporary incidence of SCD is sparse. Purpose This study aimed to evaluate the temporal trends in SCDY aged 1—49 in Denmark over 20 years. Method All consecutive SCDY in Denmark from 2000-2019 were identified by a multi-source approach, where all deaths were screened using death certificates, autopsy reports, and nationwide registry data. Deaths in individuals aged 1-35 were assessed throughout the entire study period, whereas deaths aged 36-49 were assessed from 2007-2019. Patient characteristics and causes of death were compared throughout the study period. Annual incidence rates (IR) per 100.000 person-years (p-y) were calculated using Poisson regression and corrected for age and sex by direct standardization. Temporal changes in SCD incidences were computed as annual percentage changes (APC). Results During the study period, we identified 3.206 SCD aged 1—49 years; the mean age was 42 years [IQR 33-46], and 73% were male. Over the 20-year period, patient demographics and major causes of death remained similar. The rate of witnessed SCD declined significantly from 51% to 29% (p <0.001). For SCD aged 1—35, the standardized IR decreased from 2.98/100.000 p-y (95%CI 2.34;3.75) to 1.79/100.000 p-y (95%CI 1.30;2.40), equivalent to a 42% reduction and an APC of -3.6% (95%CI -2.7;-4.5). Among SCD aged 36-49, the IR declined from 24.57/100.000 p-y (95%CI 21.70;27.71) to 10.84/100.000 p-y (95%CI 8.94;13.03), equivalent to a 56% reduction and an APC of -5.9% (95%CI -3.9;-7.9); the intergroup difference was significant (p = 0.4). Conclusion The incidence rates of SCDY declined by almost 50% during the study period for all SCDY, but the decline was significantly higher among older individuals (36-49 years). Improved resuscitation of cardiac arrests has been a critical contributor to decreasing SCD mortality, as demonstrated by the significant decline in witnessed SCDY.Incidence rates of SCD in the young