ICDs are used frequently to treat malignant ventricular arrhythmias. Despite the expanding role of these devices, little is known about the manufacturer variability in the performance of ICD generators. The purpose of this study is to explore the indications for ICD pulse generator replacement and to examine performance differences between the three major manufacturers of ICDs in the United States. The authors performed a retrospective review of ICD pulse generators that were implanted and replaced at Massachusetts General Hospital between February 1998 and March 2002. During the study period, 50 (7%) of the 707 devices in the study cohort were replaced. The most common indication for pulse generator replacement was related to battery performance followed by device recall, upgrade to a dual chamber device, and pulse generator malfunction. After exclusion of the recalled devices, a significantly higher number of pulse generators manufactured by St. Jude Medical (14/229) required replacement for battery depletion or prolonged change times during the study period compared with devices from Guidant (2/220) or Medtronic (0/273), P = 0.003 and P < 0.0001, respectively. This difference was attributable to reduced longevity in the Angstrom series of defibrillators.