Genetic diversity is enhanced by introgressing wild germplasm into breeding lines and populations. Such introgression, however, commonly introduces wild traits that must be removed by backcrossing and selection before lines are useful for elite breeding programs. Selection against wild characteristics is expected to reduce genetic diversity in introgressed lines. However, the effect of such selection on genetic diversity has not been evaluated for sugarbeet (Beta vulgaris L.). Therefore, genetic diversity was determined for 24 germplasm releases derived from cultivated sugarbeet × wild sea beet [B. vulgaris subsp. maritima (L.) Arcang.] crosses after multiple selection cycles for cultivated traits and compared to the diversity of their wild parents and cultivated sugarbeet lines using simple sequence repeat (SSR) analysis. Diversity in germplasm derived from wild × cultivated hybrids was intermediate of wild and cultivated lines in observed heterozygosity, inbreeding coefficient, and the number of alleles, private alleles, and low frequency alleles. Principal component and neighbor joining analyses demonstrated that wild × cultivated-derived germplasm shared greater similarity with cultivated germplasm than to their wild parents, while STRUCTURE analysis indicated that wild × cultivated-derived germplasm was an admixture of wild and cultivated-derived germplasm. Diversity, therefore, was enhanced in germplasm derived from wild × cultivated hybrids, although selection for cultivated traits reduced the diversity added by introgression with wild accessions. Nevertheless, the enhanced genetic diversity in germplasm releases derived from wild × cultivated hybrids identify these lines as a resource for unique genes and alleles to improve crop productivity, adaptation, and disease tolerance in sugarbeet.