Objectives To assess how much competitive sport contributes to sudden cardiac death (SCD) in young athletes and the impact on population health if this group were to be screened in the UK. Methods Using reported and imputed incidence rates of SCD in athletes and non-athletes and false-negative and false-positive test rates reported in three key Italian screening studies, the authors calculated the population and attributable risk fractions of SCD in young athletes and the total population (athletes and non-athletes) aged 12–35 years before and after screening; the number of athletes needed to screen (NNS) to prevent one SCD and the sensitivity and the specificity of screening with electrocardiogram. Using these parameters, the authors developed a decision tree model based on the UK population aged 12–35 years to estimate the annual number of SCDs, the expected number of screening and diagnostic tests and the number of athletes disqualified from competitive sport per SCD prevented. Results Participation in competitive athletics contributes to 81.9% (62.4% to 91.6%) of SCD in athletes but only 26.6% (−20.3% to 55.8%) in the total population. After screening, the contribution in the total population falls to 7.2% (−10.7% to 22.4%). The NNS is 38 151 (20 534 to 267 380). A UK screening programme would result in 1 520 021 young athletes being screened, with 140 361 referred for diagnosis. Of an expected 196 SCDs per year, 40 (6 to 74) would be prevented. For every life saved, 791 athletes would be disqualified. Conclusions The impact of screening on reducing SCD in young athletes is only modest and would be achieved with significant harms to population health.