Background: Due to high rates of ablation at the time of diagnostic EP study, follow-up of the natural history of untreated pre-excitation syndrome has become difficult. We present patients in which such data is available and study the effect of initial age on the evolution. Methods: In this retrospective review, 126 patients, 47 aged ≤19 years, 79 aged more than>19 underwent 2 similar electrophysiological studies (EPS) within 1 to 25 years of one another (8.8 ± 6.8) for occurrence of symptoms or new evaluation. First EPS was indicated for syncope (10), atrioventricular re-entrant tachycardias (AVRT) (58), atrial fibrillation (AF) (5), spontaneous PS-related adverse event (7) or asymptomatic PS (46). Results: Clinical data remained unchanged in 76 patients (60.3%). AVRT symptom was more frequently unchanged than other symptoms. Electrophysiological data remained unchanged in 105 patients (82%), but signs of initial malignant signs were variable with a disappearance in 53.5% of patients. At EPS1, AF induction was rarer in patients ≤19 years. Syncope had a low predictive value of malignant form. AVRT induction at EPS1 was not predictive of AVRT occurrence. Maximal rate over accessory pathway increased, but unexpected changes could occur. After multivariate analysis, data of first EPS were limited for the prediction of AVRT or adverse event; effect of age was not significant. Conclusions: Clinical data remained unchanged in 60.3% of patients and electrophysiological data in 82%. Initial age of evaluation did not change the modifications. Electrophysiological signs associated with sudden death varied over time. Clinical AVRT was inconstantly related to inducible AVRT (78.5%).