Periodontal diseases are common chronic inflammatory diseases caused by pathogenic microorganisms colonising the subgingival area and inducing local and systemic elevations of pro-inflammatory cytokines resulting in tissue destruction. Apparition and evolution of periodontal diseases are influenced by many local or systemic risk factors. Psychological stress has been suggested as one of them and may negatively influence the outcome of periodontal treatment. However, mechanisms explaining the possible relationship between stress and increased susceptibility to periodontal disease remain poorly understood. Several stress markers are found in blood and saliva of patients with periodontal diseases and influence the development of periodontal diseases by several mechanisms including modifications of the inflammatory response and changes in the composition of the dental biofilm. The aim of this review is to provide an insight into the relationship between psychological stress and periodontal diseases.