The purpose of this study is to emphasize the importance of service users' involvement in decision-making and service delivery process by assessing and comparing the differences in perception from service users and providers on substance abuse treatment service needs. The results of this study can be summarized into three parts as follows: First, the service users showed higher perception of service needs in medical, financial assistance, and employment services, while the service providers showed higher perception of service needs in family services. Second, the service users'perception of needs was evenly distributed into the variety service areas, while that of the service providers was concentrated on the traditional treatment services. Third, different characteristic service user groups showed different service needs; male service users showed higher service needs than female users, and the service users who had received physical treatment in the past six months showed higher needs in financial assistance and legal services than their counterparts who had not. Financial assistance and employment services were required strongly in the group who had higher numbers of legal arrests regarding substance abuse.