The oral cavity has a rich flora of bacteria; more than 500 distinct microbial species are found in dental plaque. Mycoplasma, yeast, protozoa and viruses are found in the plaque as the non-bacterial microorganism. Viruses are known to be immunosuppressive and facilitate establishment of subgingival pathogens and have been detected in the gingival crevicular fluid. Viruses infect the inflammatory cells of the periodontium and they are present more frequently in diseased sites than in healthy sites. The aim of this literature review was to report the role of viruses in periodontal diseases. Clearer understanding of roles of viruses in periodontal diseases will facilitate the provision of effective periodontal disease prevention and treatment.