The purpose of this study was to evaluate salivary Streptococcus mutans levels in patients before, during, and after orthodontic treatment. S. mutans levels were significantly elevated during active treatment. However, when sampled 6 to 15 weeks into the retention phase of treatment, the microbial levels decreased significantly to levels comparable to age-matched untreated controls. In addition, patients who were no longer wearing any retention appliances had S. mutans levels similar to those subjects sampled in the retention phase of treatment as well as to subjects in age-matched control groups. The findings of the study suggest that orthodontic treatment does not result in any long-term elevations of S. mutans levels.