OBJECTIVE: To develop an assessment of bed need that was as little affected by personal bias as possible. METHOD: The Bed Requirement Inventory (BRI) is an eight-point scale designed to identify the appropriate use of an acute psychiatric bed. This is completed by a member of the ward staff, usually a nurse, and takes 5 minutes to fill in. The reliability, validity and feasibility of using the scale in normal practice were tested in a one-year study, and variations in inappropriate bed use described. RESULTS: The inter-rater reliability of the scale was good (intra-class correlation coefficient = 0.63) and a comparison of the need for a psychiatric bed (comparing the BRI score with the judgement of an independent multidisciplinary group of professionals) also showed good agreement (k = 0.69), suggesting reasonable validity (although when the assessment was made by the named nurse agreement was less good). Results from a year-long survey in two West London hospitals showed that 17% of admissions were inappropriate and 32% had delayed discharge, black Caribbean patients had a significantly higher proportion (25%) of inappropriate admission than others (11%) and those referred from housing charities and hostels had a higher proportion (50%) of inappropriate bed use at some time than other groups (33%). CONCLUSIONS: The Bed Requirement Inventory is a quick and reliable method of determining the appropriate use of a psychiatric bed and could be of use in estimating local bed needs. Delayed discharge remains a serious reason for inappropriate bed use in London.