The caries status was recorded for 107 patients in a Norwegian psychiatric hospital in 1988. The number of edentulous patients was highest among patients older than 50 years (42%). Only two patients below 50 years of age were edentulous (5%). The average DMFT was 21.5 in the age group below 50 years and 26.8 in the age group above 50 years. The percentage number of patients with carious teeth (DT greater than 0) was 42% in those above 50 years and 60% in those below 50 years of age. On average, each patients used nearly 3 medicaments regularly. Most of the medicaments belonged to the antidepressiva and neuroleptica group which give nearly complete xerostomia. It is speculated that the reason for the high caries activity in the hospitalized psychiatric patients is due to irregular eating and oral hygiene habits in combination with complete or partial xerostomia. It is suggested that fluoride therapy (topical and tablets) and professional plaque control would be the most appropriate preventive measures.