Narrow QRS ventricular tachycardia. OBJECTIVE: To determine the frequency and clinical characteristics of narrow QRS ventricular tachycardia (QRS duration less than or equal to 0.11 seconds). DESIGN: Consecutive survey of patients with ventricular tachycardia. SETTING: Tertiary, referral-based arrhythmia service at a university medical center. PATIENTS: Sequential sample of patients with inducible ventricular tachycardia who had a 12-lead electrocardiogram of the tachycardia available for review. MEASUREMENTS AND MAIN RESULTS: Of 106 patients with ventricular tachycardia, 5 (4.7%; 95% CI, 2.1% to 10.6%) had ventricular tachycardia with a QRS duration less than or equal to 0.11 seconds. Three of the five patients were previously incorrectly diagnosed as having supraventricular tachycardia. All five patients had at least two electrocardiographic findings other than QRS duration to suggest ventricular tachycardia. CONCLUSIONS: Narrow QRS ventricular tachycardia should be considered in the differential diagnosis of narrow QRS tachycardias. Electrocardiographic findings other than QRS duration are usually present to suggest the diagnosis. 