Aims: Identification of a prolonged, corrected QT (QTc) interval in athletes may be a recommendation for disqualification from competitive sports. However, the prevalence and diagnostic significance of an isolated prolonged QTc in asymptomatic athletes without familial disease is unknown. Methods and results: Between 1996 and 2006, 2000 elite athletes (mean age, 20.2 years) underwent 12-lead ECG and 2-D echocardiography. The QT interval was corrected for heart rate (QTc). Athletes with QTc > 460 ms underwent 48 h Holter monitor and an exercise stress test. All athletes with a prolonged QTc interval were offered genetic testing and first-degree relatives were invited for ECG. The QTc was prolonged in seven (0.4%) athletes ranging from 460 to 570 ms. Three athletes had a QTc value of >500 ms and all exhibited one of: paradoxical prolongation of QTc during exercise, a confirmatory genetic mutation, or prolonged QTc in a first-degree relative. In contrast, none of the athletes with a QTc value of <500 ms had any other features to indicate long QT syndrome (LQTS). Conclusion: The prevalence of prolonged QTc in elite athletes is 0.4%. A QTc of >500 ms is highly suggestive of LQTS. A QTc of <500 ms in the absence of symptoms or familial disease is unlikely to represent LQTS in elite athletes.