Background Idiopathic ventricular arrhythmias (VAs) can be rarely ablated from the noncoronary cusp (NCC) of the aorta. Objective The purpose of this study was to investigate the prevalence and the clinical, electrocardiographic, and electrophysiologic characteristics of idiopathic NCC VAs. Methods We studied 90 consecutive patients who underwent successful catheter ablation of idiopathic aortic root VAs (left coronary cusp [LCC] 33, right coronary cusp [RCC] 32, junction between LCC and RCC 19, NCC = 6). Results NCC VAs occurred in significantly younger patients (all <40 years old) and exhibited a shorter QRS duration (all but one <150 ms), smaller R-wave amplitude ratio in leads II and III (III/II), earlier ventricular activation in the His bundle (HB) region (all but one preceded QRS onset by >25 ms), and larger atrial to ventricular electrogram amplitude ratio (A/V) at the successful ablation site (all but one >1) than the other VAs. QRS morphology of the NCC VAs was similar to that of RCC VAs, but NCC VAs always exhibited a left bundle branch block and left superior (n = 1) or inferior axis (n = 5). All NCC VAs exhibited ventricular tachycardias, although premature ventricular contractions were dominant in the other VAs. Conclusion NCC VAs were very rare (7%) and occurred in significantly younger patients than those among the other aortic root VAs. In a limited set of six patients, the ECG and electrophysiologic characteristics of NCC VAs were similar to those of RCC VAs but were characterized by narrower QRS duration, smaller III/II ratio, earlier ventricular activation in the HB region, and A/V ratio >1 at the successful ablation site. © 2013 Heart Rhythm Society.