We have documented the first microsatellites isolated from a unionid and demonstrated that these markers can be useful for surveys of neutral genetic variation in several Lampsilis species. We describe the isolation and characterization of 15 polymorphic microsatellite DNA loci for the endangered unionid Lampsilis abrupta. Among individuals from five collections, allelic diversity ranged from six to 17 alleles and averaged 10.4 alleles per locus. Individual heterozygosity was observed to range from 20.0% to 86.7% and averaged 46.9%. Cross-species amplification was investigated in nine additional Lampsilis species. A high level of flanking sequence similarity was inferred as 13 of 15 loci amplified in at least seven species.