We describe three elderly patients with Brugada-type electrocardiographic abnormalities unmasked by a high plasma concentration of the Class IC antiarrhythmic drug pilsicainide, caused by renal dysfunction. The electrocardiograms showed right bundle branch block pattern and ST segment elevation in the precordial leads in patients 1 and 2, and a polymorphic wide QRS wave in patient 3. The serum concentrations of pilsicainide were 2.85, 2.50, and 4.18 microg/ml, which were much higher than the therapeutic range (0.16-0.24 microg/ml). Withdrawal of the drug reversed the electrocardiographic changes. Careful observation is necessary to avoid life-threatening arrhythmias whenever pilsicainide is administered to elderly patients.