Purpose. The aim of this study was to assess the clinical effects of antimicrobial photodynamic therapy (aPDT) delivered as an adjunct to maintenance therapy, specifically in patients with residual pockets at previously surgically treated teeth and compare it with patients receiving mechanical debridement only. Methods and Materials. Twenty-three patients on a regular maintenance schedule who had previously received periodontal surgical care were randomly assigned to receive aPDT or a placebo at their first debridement appointment. The teeth selected had to have at least one site with bleeding on probing and a probing depth of >5mm. One week later, patients received the same treatment according to their group allocation. These teeth were simultaneously reassessed at their three- and six-month maintenance appointments. The primary outcome measure was bleeding on probing (BOP) and secondary outcome measures were plaque index (PI), probing depth (PD), and clinical attachment level (CAL). Results. There were statistically significant (SS) improvements for both groups in mean BOP, PD, and CAL. Individual sites in both groups showed SS improvements in BOP, PD, and CAL as well. When comparing the two groups directly, there was a SS increased mean PD reduction and CAL gain in the adjunctive aPDT treatment over debridement only at 6 months. There were no significant differences between the groups for BOP and PI comparisons. Conclusion. Adjunctive aPDT significantly improves PD and CAL at previously surgically treated teeth in maintenance care, when compared to mechanical debridement alone.