Differences in the use of implantable cardioverter-defibrillators (ICDs) have been reported, but the extent to which they have widened after the publication of major clinical trials supporting their use is unclear. Using data on Medicare beneficiaries, the authors determined annual age-standardized population-based utilization rates of ICDs for white men, black men, white women, and black women from 1997 to 2003. During the study period, overall use of ICDs increased most for white men (81.7-254.7 procedures per 100,000 from 1997 to 2003) and black men (38.0-151.7 procedures per 100,000), with white women (28.9-98.4 procedures per 100,000) and black women (18.2-77.3 procedures per 100,000) showing smaller increases in comparison. After adjustment with multivariable regression models, differences in utilization rates between whites and men widened compared with blacks and women between 1997 and 2003, a period when indications for ICD therapy have expanded.