Hitherto, sudden cardiac death in children (SCDc)udefined as sudden cardiac death (SCD) in the 118 years olduhas been incompletely described in the general population. Knowledge on incidence rates, causes of death and symptoms prior to death is sparse and has been affected by reporting and referral bias. In a nationwide setting all deaths in children aged 118 years in Denmark in 200006 were included. To chart causes of death and incidence rates, death certificates and autopsy reports were collected and read. By additional use of the extensive healthcare registries in Denmark, we were also able to investigate prior disease and symptoms. During the 7-year study period there was an average of 1.11 million persons aged 118 years. There were a total of 1504 deaths (214 deaths per year) from 7.78 million person-years. A total of 114 (7.5) were sudden and unexpected. A cardiac disease was known prior to death in 18 of all sudden unexpected death cases. In two-thirds of all sudden unexpected death cases no previous medical history was registered. Causes of death in autopsied cases were cardiac or unknown in 70. Unexplained deaths, presumed to be a primary cardiac arrhythmia, accounted for 28 of autopsied sudden unexpected death cases. Autopsy rate was 77. There were a total of 87 cases of SCDc (5.8 of all deaths). Prodromal symptoms were noted in 26 and antecedent symptoms in 45 of SCDc cases. The most frequent antecedent symptoms were seizures, dyspnoea, and syncope. In total, 61 of SCDc were not known with any prior disease; 23 were known with congenital or other heart disease prior to death. In total, 43 (49) of all sudden unexpected deaths died of a potential inherited cardiac disease. The incidence rate of sudden unexpected death was 1.5 per 100 000 person-years. The highest possible incidence rate of SCDc was 1.1 per 100 000 person-years. From a nationwide study of all deaths in a 7-year period more than half of all victims of SCDc experienced antecedent and/or prodromal symptoms prior to death. The incidence rate of sudden death and SCDc was 1.5 and 1.1 per 100 000 person-years, respectively. Cardiac symptoms in young persons should warrant clinical work-up and an autopsy should be performed in all cases of sudden unexpected death in which the deceased was not known with congenital heart disease prior to death. This is pivotal, in the subsequent familial cascade screening, to diagnose and treat potential inherited cardiac diseases in family members.