The poor physical health faced by people with mental illness has been the subject of growing attention, but there has been less focus on the issue of oral health even though it is an important part of physical health. This article discusses the two-way association between oral and mental health. In one direction, the prospect of dental treatment can lead to anxiety and phobia. In the other, many psychiatric disorders, such as severe mental illness, affective disorders, and eating disorders, are associated with dental disease: These include erosion, caries, and periodontitis. Left untreated, dental diseases can lead to teeth loss such that people with severe mental illness have 2.7 times the likelihood of losing all their teeth, compared with the general population. Possible interventions include oral health assessments using standard checklists that can be completed by nondental personnel, help with oral hygiene, management of iatrogenic dry mouth, and early dental referral.