Streptococcus anginosus, Streptococcus constellatus, and Streptococcus intermedius, commonly referred to as the Streptococcus anginosus group (SAG), are commensal organisms known for their propensity to cause purulent infections which are difficult to eradicate. In this study, we determined the genetic similarities between SAG isolates consecutively recovered from single patients to assess the duration of infection or colonization. A total of 97 SAG isolates recovered from 30 patients were included; 65 (67.0%) of the isolates were abscess related. The isolates were identified by the 16S rRNA reverse line blot hybridization assay as S. anginosus (n = 34), S. constellatus (n = 55), and S. intermedius (n = 8). Amplified fragment length polymorphism (AFLP) analysis of the SAG isolates produced discriminatory and reproducible patterns. Consecutive SAG isolates with identical AFLP types were found in 27 of 30 (90.0%) patients, and consecutive isolates with only a single AFLP type were demonstrated in 21 (70.0%) patients. The median delay between the times of recovery of the first and last isolates of identical AFLP types from each patient was 36 days, and this delay extended for more than 1 year in patients with both colonizing and abscess-related SAG isolates. In six bacteremic patients, paired blood and nonblood SAG isolates showed identical AFLP types.