Studies on genetic diversity in Arachis spp. using microsatellite markers have included few or no commercial cultivars among the genotypes analyzed. The primary objective of this investigation was to evaluate the utility of simple sequence repeat (SSR) markers for detecting molecular polymorphism among elite virginia-type peanut germplasm. Within that context, we had a secondary objective of assessing the impact of decades of plant breeding on allelic diversity levels among virginia-type peanut cul-tivars. All U.S. virginia-type cultivated varieties (except four) released between 1943 and 2006 were genotyped at 39 microsatellite loci. A total of 171 alleles were amplified. Allelic frequencies ranged from 0.02 to 0.97, with an average of 0.27. Although no significant difference was observed for the number of alleles present between the initial and the most recent time periods, our results indicate that levels of diversity present in virginia-type peanuts have fluctuated significantly since the 1940s and peaked during the 1970s. Our study demonstrates that microsatellite markers may be useful for detecting molecular variation among peanut cultivars. Moreover, this is the first report of using micro-satellite markers to describe genetic diversity in a collection of cultivated varieties of peanut. © Crop Science Society of America.