Older people with mental health problems frequently have complex needs related to the common co-existence of physical health and social care problems. Effective evaluation of long-term and multiple problems may be particularly difficult without standardised methods aimed at comprehensive and systematic assessment of needs. Until this project there existed no instrument specifically designed to measure comprehensively the needs of older people with mental health problems. The development of such an instrument which would take account of patients', staff and carers' views on needs is described. Following an extensive development process which included focus groups, a modified Delphi process and a consensus conference, the assessment instrument was subjected to a test-retest and inter-rater reliability study while aspects of validity were addressed both during development and with data provided by sites in the UK, Sweden and the USA. The Camberwell Assessment of Need for the Elderly (CANE) comprises 24 items (plus two items for carer needs), and records staff, patient and carer views. It has good content, construct and consensual validity. It also demonstrates appropriate criterion validity. Reliability is generally very high (e.g. kappa [greater than] 0.85 for all Reynolds 2003 CANE Thesis Abstract staff ratings of inter-rater reliability). Correlations of inter-rater and test-retest reliability of total numbers of needs identified by staff were 0.99 and 0.93, respectively. The psychometric properties of the CANE seem to be highly acceptable. It was easily used by a wide range of professionals without formal training. Interest in the CANE has resulted in its translation into five other European languages so far (Swedish, Spanish, German, Norwegian and Dutch) and several more translations are planned. The study shows that it is a tool with good reliability and validity for comprehensively measuring the needs of older people with mental disorders. Its popularity has resulted in its widespread use in research and clinical practice around the world.