Although oral health is a major determinant of general health and quality of life, it has a low priority in the context of mental illness. Chronic mental illness and its treatment carry inherent risks for significant oral diseases. Both the disease itself and its various pharmacologic management modalities lead to a range of oral complications and side effects, with caries, periodontal disease and xerostomia being encountered most frequently. Older age, female gender, length of hospitalization, duration of mental illness, psychiatric diagnosis are the most discussed predictors for adverse dental outcomes in the reviewed studies. Poor oral hygiene, higher intake of carbonates, smoking, poor perception of oral health self-needs, length of psychiatric disorder, length of psychotropic treatment, and less access to dental care pose at high risk for poor oral health among this population. This article emphasizes the importance of preventive dentistry programs to improve dental healthcare psychiatric chronic inpatients and the signifance of bridging dental health education to psychiatric rehabilitation programs. In this review, general information concerning the oral manifestations of mental illness, effect of medication of mental illness on oral health, the factors affecting oral health among this special population have been provided.