BACKGROUND: delirium is under-diagnosed and under-treated in comparison to other common and serious acute disorders. The reasons for this are unclear. OBJECTIVE: we conducted a multicentre survey of knowledge of and attitudes to delirium in trainee general physicians. DESIGN: questionnaire-based survey in 34 acute hospitals in the UK. METHODS: we developed a questionnaire designed to test knowledge of delirium prevalence, DSM-IV diagnostic criteria, use of specific screening tools, association with adverse outcomes, and pharmacological management. Questionnaires were completed and returned by hand to the researchers immediately after recruitment. Participants were a convenience sample of trainee doctors in general and emergency medicine. RESULTS: 784 trainee physicians participated. Most participants expressed the view that delirium has a high prevalence and that it is associated with serious adverse outcomes. However, they had poor knowledge of its diagnosis and treatment, reporting the need for better training. Experience working in geriatric medicine had only a modest effect on the ability to diagnose delirium. CONCLUSIONS: UK training doctors' lack of basic knowledge of the diagnosis and management of delirium, rather than a lack of awareness of its high prevalence and clinical significance, appears to be important in determining its under-recognition.