Aim: To evaluate (1) whether periodontitis has an influence on the prevalence/ incidence of respiratory diseases (chronic obstructive pulmonary disease [COPD], asthma, community-acquired pneumonia [CAP], obstructive sleep apnoea [OSA] and COVID-19), and ( 2) what is the impact of periodontal therapy on the onset or progression of respiratory diseases.Materials and Methods: An electronic search was performed on Pubmed, Cochrane Library and Scopus databases up to October 2021, to identify studies answering the PECOS and PICOS questions.Results: Seventy-five articles were selected. Meta-analyses identified statistically significant associations of periodontitis with COPD (n studies = 12, odds ratio [OR] = 1.28, 95% confidence interval [CI] [1.16; 1.42], p < .001), and OSA (n s = 6, OR = 1.65, 95% CI [1.21; 2.25], p = .001), but not for asthma (n s = 9, OR = 1.53, 95% CI [0.82; 2.86], p = .181). For acute conditions, two studies were found for CAP, while for COVID-19, significant associations were found for the need of assisted ventilation (n s = 2, OR = 6.24, 95% CI [2.78; 13.99], p < .001) and COVID-related mortality (n s = 3, OR = 2.26, 95% CI [1.36, 3.77], p = .002). Only four intervention studies were found, showing positive effects of periodontal treatment on COPD, asthma and CAP.Conclusions: A positive association between periodontitis and COPD, OSA and COVID-19 complications has been found, while there is a lack of intervention studies.