Multidimensional functional assessment is the basis of individualized care. It is especially important in the care of elderly, with the complexity of symptomatology and often with cognitive impairment present. An assessment instrument for elderly persons, used in this study, is the Resident Assessment Instrument/Minimum Data Set (RAI/MDS) and its incorporated MDS Cognitive Performance Scale (CPS). The purposes of the study were to demonstrate the cognitive performance in elderly persons in different levels of care by using the CPS and to elicit the views of staff on use of the RAI/MDS. Cognitive impairment was found in 1276 elderly persons in six levels of care studied, an important factor to consider when organizing care of elderly. An intervention study was carried out for 1 year in three nursing home wards, with training and supervision in implementation of the RAI/MDS including individualized and documented care. Part of a questionnaire was used to evaluate staff (n = 50) views on using the instrument. A majority of the staff thought that the RAI/MDS could contribute to the improvement of quality of care, documentation in nursing records, and in co-operation and engagement. Further research is necessary to elicit more knowledge on the usefulness and benefits of the instrument.