The Resident Assessment Instrument (RAI) is described. The RAI consists of three basic components: 1) the Minimum Data Set (MDS) is a collection of items covering all the areas one would expect when assessing the needs of elderly people and developing a care plan, 2) the Resident Assessment Protocols are a series of protocols which guide the assessor through the best practice of care planning for the common problems faced by the elderly and 3) the Resource Utilization Groups is a classification system based on MDS to predict resource use at the level of the individual resident. The goal of RAI is to improve the quality of care. It also enables national and international comparisons between long term care residents. RAI was used at 65 nursing homes in Copenhagen in 1992-93 and 3451 residents were examined. The reproducibility and validity of the instrument was tested and found to be good. Results from the use of RAI in Denmark is presented. We conclude that RAI is useful in assessing residents at nursing homes, because the collected data triggers actions that improve the quality of care.