Atrioventricular nodal reentrant tachycardia and accessory pathway-mediated tachycardia may have different ages of tachycardia onset. Symptom onset data were obtained in 519 patients (atrioventricular nodal reentrant tachycardia, 231, accessory pathway-mediated tachycardia, 288). The mean age of the patients at the time of evaluation was 47 +/- 17 years (atrioventricular nodal reentrant tachycardia) and 37 +/- 15 years (accessory pathway-mediated tachycardia). The mean age of symptom onset was 32 +/- 18 years for atrioventricular nodal reentrant tachycardia and 23 +/- 14 years for accessory pathway-mediated tachycardia. A significantly greater proportion of patients with atrioventricular nodal reentrant tachycardia had the initial onset of symptoms after the age of 20 years (atrioventricular nodal reentrant tachycardia, 67% vs accessory pathway-mediated tachycardia, 41%, p < 0.001). In summary, there is a different mean age of symptom onset for patients with atrioventricular nodal reentrant tachycardia and accessory pathway-mediated tachycardia.