Long-term follow-up data on young patients receiving amiodarone is lacking, especially in relation to growth and late side effects. The records of 95 young patients (mean age 12.4 years; range 3 weeks to 31.5 years) who received amiodarone were reviewed. Minimal follow-up time for those continuing to take amiodarone was 1.5 years; the mean duration of therapy was 2.3 years (maximal 6.5). The mean maintenance dosage was 7.7 (1.5 to 25) mg/kg body weight per day. Initial success (based on symptoms and 24 h electrocardiogram) was achieved in 23 of 34 patients with ventricular tachycardia, in 32 of 33 with atrial flutter and in 21 of 28 patients with supraventricular tachycardia. However, in 7 of 33 patients with atrial flutter, the arrhythmia returned after 6 months. Patient growth continued in the same percentiles achieved before amiodarone in all but eight patients, improving in six and worsening in two with severe underlying disease. Proarrhythmia occurred in three patients: one had torsade de pointes that disappeared when amiodarone administration was stopped; two with severe anatomic heart disease died suddenly during the loading period (one with atrial flutter and one with ventricular tachycardia). Side effects occurred in 28 (29%) of the 95 patients: keratopathy (in 11), abnormal thyroid function test (in 6), chemical hepatitis (in 3), rash (in 3), peripheral neuropathy (in 2), hypertension (in 1) and vomiting (in 1). All side effects disappeared when amiodarone was discontinued or the dose was reduced.(ABSTRACT TRUNCATED AT 250 WORDS)