We report a patient who experienced a reversible prolongation of the QT interval and episodes of syncope while receiving probucol. A 64-year-old woman experienced syncopal attacks 8 and 11 weeks after beginning probucol treatment (500 mg twice daily). The pre-treatment ECG showed a slight prolongation of the corrected QT interval (QTc) (0.46 sec). Her QTc increased to 0.62 sec 12 weeks after beginning probucol treatment and decreased to about the baseline value (0.48 sec) 6 weeks after treatment was discontinued. Probucol is known to prolong the QT interval. A long QT interval has been linked to an increased risk of ventricular arrhythmias, syncope or sudden death. However, clinical reports which causally relate probucol treatment to syncope are very rare. Although an ECG during the episodes of syncope was not available, this patient's syncope might be due to ventricular tachyarrhythmia associated with probucol-induced QT prolongation. This case emphasizes the need for careful evaluation of the QT interval before and during probucol treatment.