Computerized reminder systems have been shown to be effective in improving physician compliance with preventive services guidelines. Very little has been published about the use of computerized reminders for preventive care in diabetes. We implemented a computer-generated reminder system for diabetes care guidelines in a randomized controlled study in the outpatient clinics of 35 internal medicine residents at the University of Utah and Salt Lake Veterans Affairs Hospitals. After a six month study period, compliance with the recommended care significantly improved in both the intervention group that received patient-specific reminders about the guidelines (38.0% at baseline, 54.9% at follow-up) and the control group that received a nonspecific report (34.6% at baseline, 51.0% at follow-up). There was no significant difference between the two groups. Both clinic sites showed similar improvement over baseline levels of compliance. Residents who completed encounter forms used by the system showed a significantly greater improvement in compliance than those who did not complete encounter forms (19.7% vs. 7.6%, p = 0.006). The improvements in guideline compliance were seen in all areas of diabetes preventive care studied, and significant improvements were seen with recommended items from the medical history, physical exam, laboratory testing, referrals, and patient education. The use of encounter forms by the providers significantly improved documented compliance with the guidelines in almost all categories of preventive care. These results suggest that computerized reminder systems improve compliance with recommended care more by facilitating the documentation of clinical findings and the ordering of recommended procedures than by providing the clinician with patient-specific information about guideline compliance status. Further study is needed to understand the implications of these findings to the development of future computerized reminder systems for chronic diseases such as diabetes.