This case study paper reports on the development and implementation of DISXPERT, a rule-based expert system tool for referral of social security disability recipients to vocational rehabilitation services. The growing use of paraprofessionals as caseworkers responsible for assessment in the social services area provides fertile domain areas for new and innovative application of expert systems technology. The main function of DISXPERT is to provide support to paraprofessional caseworkers in reaching unbiased and consistent assessment decisions regarding referral of clients to vocational rehabilitation services. The results after three years of use demonstrate that paraprofessional using DISXPERT can make assessments in less time and with a level of accuracy comparable to the vocational rehabilitation domain professionals using manual methods. This case study paper discusses the problem domain, the design and development of the system, uses of AI technology, payoffs, and deployment and maintenance of the system.