Clinical characteristics and long-term prognosis of 163 children with ventricular arrhythmias without underlying heart diseases(78 with ventricular premature contractions(VPC group), 39 with ventricular couplets(CPLT group), and 46 with ventricular tachycardia(VT group))were studied by Holter electrocardiographic monitoring(Holter ECG)and treadmill exercise testing The age of the subjects at the initial examination was 8.9±3.4 years in the VPC group, 9.9±3.5 years in CPLT group, and 9.4±3.1 years in the VT group. The duration of the follow-up was 71.7±32.1 months in the VPC group, 65.9±32.8 months in the CPLT group, and 84.0±31.9 months in the VT group. VPC's disappeared during the follow-up period in 22(28%)of the 78 children in the VPC group. CPLT's disappeared in 15(38%)and VPC's disappeared in 9(23%)of the 39 children in the CPLT group. In the 46 children in the VT group, VT disappeared in 30(65%), and VPC's disappeared in 17(37%). One child(2%)in the VT group died of heart failure due to drug-resistant sustained VT. The mean time until the disappearance of VPC's in the 163 patients was estimated to be 115.2±4.3 months. The mean time until the disappearance of VT in the 46 children in the VT group was estimated to be 89.0±4.9 months. Multivariate analysis of prognostic factors related to the disappearance of VPC's indicated that nighttime VPC's were significantly more likely to disappear(p=0.018), and that symptomatic VT was significantly more likely to disappear than asymptomatic VT(p=0.032), probably because more symptomatic cases received antiarrhythmic therapy. Ventricular arrhythmias in children without underlyng diseases often disappeared, and the prognosis was generally favorable. However, appropriate treatment and follow-up were required in children with sustained VT, symptomatic VT, or VT with a high rate of VT.