This study investigated the genotype diversity of Prevotella isolates from dentoalveolar abscess and the genetic relatedness between clinical and commensal isolates within the same patients. Prevotella strains recovered from pus and dental plaque of individual patients (n=9) were examined.Each specimen was inoculated on to blood agar. Six to ten presumptive Prevotella colonies per specimen grown on the primary culture plate were selected. The colonies were genotyped using a random amplified polymorphic DNA assay and the antimicrobial susceptibility profile were also determined. Multiple genotypes per organism were evident in both pus (9 of 9 patients) and plaque (3 of 9 patients). The same genotype wasshared by pus and plaque strains in 6 of the 9 patients, while no genetic agreement between pus and plaque strains occurred in the remaining 3 patients. Although it has been suggested that the microflora of infection sites is comprised of genetically homogeneous strains, these findings indicate that a wide range of genetic heterogeneity occurs in infecting Prevotella strains. Furthermore, although dentoalveolar abscess is an opportunistic infection involving endogenous oral bacteria, only certain strains from the commensal population might be involved in the infection.