To characterise the demographics and aetiology of sudden cardiac death (SCD) in athletes referred to a tertiary cardiac pathology centre in the UK. Retrospective non-case controlled analysis. Cardiac pathology centre at the National Heart and Lung Institute and Royal Brompton Hospital. Between 1996 and 2008, the hearts of 118 athletes were referred for pathological assessment to ascertain the precise aetiology of SCD. The majority of athletes (n = 113; 96%) were male and most (107; 91%) were amateurs participating predominantly in football, rugby and running. The mean (SD) age of death was 28 (12) years (range 7-59); 75% athletes were aged < or =35 years. Most deaths (81%) occurred during or immediately after exercise. Antecedent symptoms of cardiac disease were reported in 21 (18%) subjects, and 20 (17%) had a family history of premature cardiovascular disease and/or SCD. 25 (21%) athletes had relevant past medical history which included a known history of cardiac disease. Cardiomyopathy was the commonest cause of death and accounted for 62% of all the SCDs. A significantly high proportion of athletes (23%) exhibited a morphologically normal heart. Atherosclerotic coronary disease accounted for only 3% of cases and was confined to athletes aged >35 years. SCD in sport is largely due to clinically silent cardiomyopathies or primary electrical disorders (morphologically normal heart). Antecedent symptoms and family history are absent in over 80% of cases, and therefore clinical screening with health questionnaires will fail to identify most athletes with potentially sinister cardiac disorders.