Although dentists are beginning to use computers in their offices for billing, insurance, and word processing, applications in computer-assisted diagnosis have not developed as rapidly. In medicine, use of computer-assisted techniques leads to more accurate and timely diagnoses and improves the quality of patient care through reduction in morbidity and increased physician interaction with patients. This article describes and discusses a system which, though developed for medical diagnosis, has very real applicability in dentistry. This PC-based, expert system takes variable input from the patient and links it with a large fixed database that is designed to deal with a specific patient problem. Output in the form of suggested causes and/or management options is delivered to the practitioner. Several modules have been developed and are ready for clinical use. The module "Periapical Radiolucency" will be described in this article to illustrate some of the characteristics of this system.