Objective: The development of a simple, comprehensive, valid and reliable tool to assist aged care services staff develops and monitors care plans. Method: An assessment with proven utility in a psychogeriatric setting was modified to improve its relevance to aged care services. Reliability was assessed from the scores obtained from two independent raters assessing 48 randomly selected residents in a large aged care facility. Validity was assessed by comparison with well-validated measures of cognition and function. Results: The Care Planning Assessment Tool has very high interrater reliability and good internal consistency. The validity of the subscales compared with well-validated assessments was very high. Conclusion: The psychometric properties of the Care Planning Assessment Tool are sufficiently good to allow it to be used with confidence in the care planning process. This is supported by a similar evaluation carried out on the Japanese version.