Context: Computerized systems to remind physicians to provide appropriate care have not been widely evaluated in large numbers of patients in multiple clinical settings. Objective: To examine whether a computerized reminder system operating in multiple Veterans Affairs (VA) ambulatory care clinics improves resident physician compliance with standards of ambulatory care. Design, Setting, and Participants: A total of 275 resident physicians at 12 VA medical centers were randomly assigned in firms or half-day clinic blocks to either a reminder group (n=132) or a control group (n=143). During a 17-month study period (January 31, 1995-June 30, 1996), the residents cared for 12989 unique patients for whom at least 1 of the studied standards of care (SOC) was applicable. Main Outcome Measures: Compliance with 13 SOC, tracked using hospital databases and encounter forms completed by residents, compared between residents in the reminder group vs those in the control group. Results: Measuring compliance as the proportion of patients in compliance with all applicable SOC by their last visit during the study period, the reminder group had statistically significantly higher rates of compliance than the control group for all standards combined (58.8% vs 53.5%; odds ratio [OR], 1.24; 95% confidence interval [Cl], 1.08-1.42; P=.002) and for 5 of the 13 standards examined individually. Measuring compliance as the proportion of all visits for which care was indicated in which residents provided proper care, the reminder group also had statistically significantly higher rates of compliance than the control group for all standards combined (17.9% vs 12.2%; OR, 1.57; 95% Cl, 1.45-1.71; P<.001) and for 9 of the 13 standards examined individually. The benefit of reminders, however, declined throughout the course of the study, even though the reminders remained active. Conclusions: Our data indicate that reminder systems installed at multiple sites can improve residents' compliance to multiple SOC. The benefits of such systems, however, appear to deteriorate over time. Future research needs to explore methods to better sustain the benefits of reminders.