The electronic medical record (EMR) will constitute the core of a computerized health care system in the near future. The electronic storage of clinical information will create the potential for computer-based tools to help clinicians significantly enhance the quality of medical care and increase the efficiency of medical practice. These tools may include reminder systems that identify patients who are due for preventative care interventions, alerting systems that detect contraindications among prescribed medications, and coding systems that facilitate the selection of correct billing codes for patient encounters. Numerous other "decision-support" tools have been developed and may soon facilitate the practice of clinical medicine. The potential of such tools will not be realized, however, if the EMR is just a set of textual documents stored in a computer, i.e. a "word-processed" patient chart. To support intelligent and useful tools, the EMR must have a systematic internal model of the information it contains and must support the efficient capture of clinical information in a manner consistent with this model. Although commercially available EMR systems that have such features are appearing, the builders and the buyers of EMR systems must continue to focus on the proper design of these systems if the benefits of computerization are to be fully realized.