Until recently, the care services for disabled persons have been under rigid control by public sectors in terms of provision and funding in Japan. A reform was introduced in 2003 that brought a rapid increase of utilization of services and serious shortage of financial resources. Under these circumstances, the "Services and Supports for Persons with Disabilities Act" was enacted in 2005, requiring that the care service provision process should be transparent, fair and standardized. The purpose of this study is to develop an objective tool for assessing the need for disability care. In the present study we evaluate 1423 cases of patients receiving care services in 60 municipalities, including all three categories of disabilities (physical, intellectual and mental). Using the data of the total 106 items, we conducted factor analysis and regression analysis to develop an assessment tool for people with disabilities. The data revealed that instrumental activities of daily living (IADL) played an essential role in assessing disability levels. We have developed the uniformed assessment tool that has been utilized to guide the types and quantity of care services throughout Japan.