Introduction: Most studies on Sudden Cardiac Death (SCD) in the young are based on samples in selected groups and the death of athletes is a rare but devastating occurrence.We here present two nationwide studies (population 5.4 million) on the incidences of SCD (1-35 years old) and sport related SCD (SrSCD) in the 12-35 years old by systematic evaluation of all deaths.Methods: All deaths in Denmark from 2000-2006 in the 1-35 years old were included.The death certificates were reviewed independently by two physicians.Information on previously known disease was retrieved from The National Patient Registry.The number of persons autopsied was ascertained and autopsy reports were read.Cause of death was revised based on autopsy findings.We defined SCD as a natural non-traumatic sudden death of cardiac cause occurring in a person last seen alive and well 24 hours prior to death.Results: SCD: We identified 625 cases of possible SCD (10% of all deaths), of which 156 (25%) were not autopsied (presumed SCD).Of the 469 autopsied cases, 314 (67%) were SCD.Most common cardiac cause of death was ischemic heart disease (13%); 29% of autopsied possible SCD cases were unexplained (SUD).In 45% of SCD cases the death was witnessed; 34% died during sleep; 89% were out-of-hospital deaths.Combined incidence rate of definite SCD,SUD and presumed SCD in the young was 2.8 per 100 000 person-years, this being the highest possible incidence rate.Excluding presumed SCD cases the incidence rate declined to 1.9 per 100 000 person-years.SrSCD: Fifteen (range 0-5 per year) cases of SrSCD were found, 8 of which had antecedents symptoms.The incidence rate was 1.21 (95% CI 0.68-2.00) per 100 000 athlete person-years.Most common autopsy findings were: arrhythmogenic right ventricular cardiomyopathy (n=4), sudden unexplained death (n=4) and coronary artery disease (n=2).The incidence of SCD in the general population age 12-35 was 3.76 (95% CI 3.42-4.14) per 100 000 person-years.Conclusions: These two studies are probably the most thorough on SCD in the young, allowing the studies to report precise incidence rates on presumed and definite SCD in the young.Of the presumed SCD victims 76% were autopsied.Autopsy-negative cases (SADS) were common.In Denmark sports related sudden cardiac death is a rare occurrence and the incidence rate is lower than that of sudden cardiac deaths in the general population.Reference: Holst AG, Winkel BG, Theilade J, Kristensen IB, Thomsen JL, Ottesen GL, Haunso SH, Svendscn JH,Prescott E and Tfelt-Hansen J Incidence and etiology of Sports Related Sudden Cardiac Death in Denmark-Implications for preparticipation screening.Heart Rhytm 2010 DO I: 10.1016.