Ventricular couplets may be a risk factor for sudden death in adults, but their prognosis in children is unknown. From 1981 to 1987 104 patients, mean age 13.2 years (0.2 to 37 years), had ventricular couplets on a 24-hour electrocardiogram (ECG) (Holter monitor) and on follow-up with a second Holter (mean, 2.5 years). Of the 104 patients, 22 had a normal heart and 82 had an abnormal heart. Patients with a normal or an abnormal heart did not differ in incidence or severity of symptoms (patients with a normal heart had 17 instances of palpitations and none of syncope; patients with an abnormal heart had 49 instances of palpitations, six of dizziness, and none of syncope). Number of ventricular couplets was higher in patients with a normal heart (33±50/day: mean ±1 SD) than in those with an abnormal heart (17±15/day; p<0.05). Of the 22 patients with a normal heart, 11 underwent an electrophysiologic study (EPS); none had inducible ventricular tachycardia. After mean follow-up of 29.7 months, all 22 patients with a normal heart were alive without ventricular tachycardia; 6 of 22 were treated for palpitations, with complete suppression of couplets in two. In 11 of 16 untreated patients with a normal heart, ventricular couplets disappeared spontaneously. Of the 82 patients with an abnormal heart, 32 had an EPS: nine (28%) had sustained ventricular tachycardia, 16 (50%) had nonsustained ventricular tachycardia, and seven (22%) had no inducible ventricular tachycardia. ECG criteria and hemodynamic status were of limited value in predicting inducibility of ventricular tachycardia. Two of 82 patients with an abnormal heart had sudden death with documented ventricular tachycardia/fibrillation; 59 of 82 were treated, with success in 55; 23 were not treated, with spontaneous disappearance of ventricular couplets in 10. As a result of this study, we reached the following conclusions. (1) Ventricular couplets appeared benign in patients with a normal heart. (2) in patients with an abnormal heart, inducible ventricular tachycardia was common (78%). (3) Sudden death occurred in 2 of 82 patients with an abnormal heart within less than 3 years of detection of couplets. (4) Thus the prognosis of ventricular couplets in the young may be related to the underlying substrate. © 1990.