6 cases of accidental astemizole poisoning in children have been reported to the Finnish Poison Information Center. The children were aged 1 year 7 months to 3 years 4 months and had taken doses of 2.5 to 16.7 mg/kg, at least twelve times that recommended. In 2 children the overdose was verified by measurement of drug concentrations. Despite measures to prevent drug absorption prolonged QTc-interval, a sign of cardiac toxicity, was found in all 5 children on whom an electrocardiogram was available for analysis, and severe ventricular arrhythmias developed in 1. Young children with accidental astemizole overdose should be carefully monitored in hospital. Similar precautions may be justified in cases of overdose with other selective H1-histamine receptor antagonists.