Antimicrobial photodynamic therapy (aPDT) has been widely used in Periodontics to obtain reduction of periodontopathogenic bacteria with absence of systemic side effects and minimal bacterial resistance. Therefore, a good adjuvant alternative for periodontal disease treatment arises, especially for patients with Down syndrome (DS) who present greater severity and high prevalence of periodontal disease. Usually aPDT is used as an adjunct therapy to scaling and root planning.