Trichomonas tenax is a flagellated, aerotolerant protozoan that lives in the human oral cavity and is distributed between the teeth, gums, tongue and saliva of people with poor oral hygiene. The presence of this protozoan is considerably high in persons with more dental calculus, coated tongue and poorly-cleaned periodontal tissue rather than in individuals with clean and healthy oral cavities. T. tenax has been implicated in the aetiology of several infections outside of the oral cavity, being detected in cerebrospinal fluid samples from patients diagnosed with polymicrobial meningitis, in the salivary duct infecting the sub-maxillary glands, and causing pulmonary eosinophilia in bronchoalveolar fluid. T. tenax has also been identified in fibrocystic mastopathy, in a infra-auricular lymph nodes causing cervical adenopathy, in sputum samples of immunocompromised patients with chest pain and chronic lung diseases causing pulmonary trichomoniasis, and in pleural empyema samples from upper respiratory tract infections. Although T. tenax has been detected in dental calculus and subgingival dental plaque, its role in the physiopathology and the mechanism involved on tissue damage of oral infections are still unclear. In addition, T. tenax presence in the oral cavity has been associated with periodontal disease; however, its role in this pathology is also unclear.