OBJECTIVES:To describe the prevalence of oral diseases and their impact on oral-health-related quality of life in people with severe mental illness undertaking community-based psychiatric care. METHODS:A survey was conducted at eight outpatient psychiatric care clinics in Tower Hamlets, London, UK. One hundred and twelve consecutive patients with mental illness were invited to participate in this study. They were clinically examined and asked to complete the oral health impact profile (OHIP) questionnaire. RESULTS:The response rate was 79% (n = 89); 57 (64%) males and 58 persons over 45 years of age (65%) participated in this survey. Overall OHIP score was 25.4 (95% CI 23.3, 27.4), 70 (78%) were smokers and 45 (51%) had been to the dentist in the last two years. Forty-seven (53%) respondents had caries in at least one tooth, 60 (67%) had 21 teeth and more, and 14 (16%) used dentures. Advanced periodontal treatment was indicated in 42 (55%) of patients and 52.8% (n = 47) patients reported current pain. CONCLUSION:Overall, this survey found that oral health has a great impact on patients with severe mental illness being treated in the community setting and their oral health is poorer than the national adult general population. Future research should consider the causes that relate to the poorer oral health in this population and potential health promotion mechanisms in this population to encourage an upstream approach to health.