Sudden death during sports activities, although unfrequent, is a tragic event with great impact on both the general and medical communities. The two commonest conditions leading to sudden cardiac death in young athletes are hyperthrophic cardiomyopathy (HCM), the main cause in the USA, and arrythmogenic right ventricular cardiomyopathy, which is the leading cause in Europe. We report the case of a 17-year-old football player with a pathological electrocardiography (ECG) in the pre-participation screening programme, highly suggestive of HCM, in which ECG study showed a septum thickness of 28 mm. Genetic analysis revealed R 495 W mutation in the 18 exon of the MyBPC3 (myosin-binding protein C) and sports activities were contraindicated. Two years later, septum thickness was 19.5 mm. Usefulness of 12-lead ECG, differential diagnosis between athlete's heart and HCM, and the stratification in patients with HCM are discussed.