© 2016 Japanese College of Cardiology Idiopathic ventricular arrhythmias (VAs) are ventricular tachycardias (VTs) or premature ventricular contractions (PVCs) whose mechanisms are not related to myocardial scar. Idiopathic VAs occur most commonly without structural heart disease, but can occur with structural heart disease. Imaging tests, such as echocardiography, nuclear test, and cardiac magnetic resonance imaging, are helpful for excluding any association of an idiopathic VA occurrence with myocardial scar. Since catheter ablation emerged, the sites of idiopathic VA origins, commonly endocardial but sometimes epicardial, have been increasingly recognized. Idiopathic VAs usually originate from specific anatomical structures, and exhibit characteristic electrocardiograms based on their anatomical background. Idiopathic VAs are basically benign, but they require medical treatment or catheter ablation when idiopathic VAs are symptomatic, incessant, or produce left ventricular dysfunction. This review describes the up-to-date information on the prevalence of idiopathic VA origins relevant to the anatomy, and diagnosis, and treatment of idiopathic VAs.