Little information is available regarding the oral health of hospitalized psychiatric patients. The aims of the study were: • to quantify the oral health status and identify dental treatment needs of hospitalized psychiatric patients in South Wales; and • to compare the oral health of subgroups within the population by their age, psychiatric diagnosis, psychotropic medication use, and length of stay. The total patient population of the hospitals involved in the study was 469, and 326 subjects (70%) took part in the study. The mean age of the subjects was 71.1 years, with 265 long-stay and 61 short-stay patients. Forty-seven percent of patients had a psychiatric diagnosis of dementia, 23% of schizophrenia, and 19% of depressive illness. The examination included assessment of oral hygiene, periodontal condition, and prevalence of caries. The treatment needs of the population were also determined. It was found that 63% of the population was edentulous. The mean DMFT score was 19.1 ± 7.9 (SD). Comparison with the DMFT of the general population showed a similar level of decay, fewer filled teeth, and more missing teeth in the study population. The oral hygiene of the dentate population was poor, and there was little periodontal disease. Treatment needs were mainly for scaling and polishing. There were no significant differences found between subgroups within the population.