The fitness of patients with Wolff-Parkinson-White syndrome to indulge in sporting activities is a practical cardiology problem. The major risk is sudden death due to atrial fibrillation deteriorating to ventricular fibrillation. This risk is small or even theoretical, but signing a fitness certificate engages the clinician's responsibility. Non invasive complementary examinations are useful. Echocardiography may detect a heart disease that would preclude any sport. Exercise tests explore the behaviour of the accessory pathway and rarely trigger off arrhythmias. Holter recordings mainly investigate disorders of the atrial rhythm. The decision concerning fitness may be based on clinical symptoms. Exercise-induced tachycardia is a classical contra-indication to competitive sports. In patients whose tachycardia is unrelated to exercise, fitness may be discussed according to the results of exercise tests and of the electrophysiological study. A refractory period which would be considered as rather prolonged at rest does not protect against fast ventricular rate during passage to atrial fibrillation. If pre-excitation disappears during the exercise test in an asymptomatic patient, then competitive sports can be authorized without limitations. If not, only surgical excision or fulguration would provide full protection against a potentially dangerous fibrillation. It is concluded that Wolff-Parkinson-White syndrome contra-indicates competitive sports in most cases. Games played outside competitions remain possible in the absence of symptoms or when arrhythmias are well controlled by medical treatment.