Computer programs to assist with medical decision making have long been anticipated by physicians with both curiosity and concern. This article summarizes the current status of computer-based medical decision support, the goals of system developers, the reasons for slow progress since the field began almost 30 years ago, and the logistical and scientific challenges that lie ahead. It emphasizes in particular that decision-support programs are intended to serve as tools for trained practitioners who retain ultimate responsibility for determining diagnostic and therapeutic strategies.