Diabetes care among medically underserved patients is suboptimal. Few studies, however, have described successful strategies to improve diabetes care in these patient populations. To address this issue, 4 Montana community health centers and 1 urban Indian health center implemented quality improvement efforts along with an office-based electronic system for monitoring diabetes care. After a median of 17 months follow-up, preventive services and clinical outcomes were assessed for all patients at baseline (N = 332) and follow-up (N = 590), and for a cohort (N = 164) who had 1 or more visits 6 months after baseline. In cross-sectional analyses, there were increases from baseline to follow-up in the percent of patients who had received an annual foot examination (50% to 68%), microalbuminuria testing (34% to 62%), annual retinal examination (14% to 30%), pneumococcal immunization (30% to 61%), and smoking assessment (77% to 91%). But neither HbA1c testing in the previous 6 months (64% to 55%) nor annual LDL-C testing (59% to 61%) showed any improvement. There were no significant changes from baseline to follow-up in the median hemoglobin A1c (HbAlc), low density lipoprotein-cholesterol (LOL-C), or in systolic and diastolic blood pressure values. Similar improvements in preventive care were seen in the cohort of patients with diabetes. But overall outcomes were not improved. Our findings suggest that office-based monitoring systems can support systems' changes to improve the delivery of preventive services to patients with diabetes in primary care facilities for the underserved, but outcomes are more difficult to enhance over a short period of follow-up. Also, our findings suggest that over a relatively short-term period, cross-sectional and cohort analyses of quality improvement measures do yield similar measures of diabetes care in such settings.