Since 1988 to 1992 we analyzed 116,452 consecutive 12-lead electrocardiograms belonging to the entire cohort of 18-year old young boys resident in Padova, Treviso, Rovigo, Venezia, Belluno area (2,834,000 inhabitants). We identified 173 cases of overt WPW pattern (short PR interval, delta wave, anomalous configuration of QRS complex) with a calculated incidence of 1.48/1000. Accessory pathway location was: left free wall (70 patients), right free wall (39 patients), postero-septal (37 patients), antero-septal (15 patients) and undetermined (12 patients). Sixty patients (34.6%) complained of different symptoms as palpitations, near syncope and dizziness. Fifty-three patients (30.6%) went in a regular sport activity. Twenty-four hour Holter monitoring (41 patients) and exercise stress test (43 patients) did not show sustained tachyarrhythmias; intermittent preexcitation was recorded in 23 and 32 patients, respectively. Two-dimensional echocardiogram (68 out of 173) was normal in 44 patients, while 24 showed minor cardiac abnormalities with two major disease; mitral valve prolapse was diagnosed in 8 patients. On the basis of transesophageal (24 patients) or intracardiac (5 patients) electrophysiologic study, 11 patients were considered at high risk for sudden death. Eight of them suffered from spontaneous symptoms.