Objective: To assess the impact of a decision aid on perceived risk of heart attacks and medication adherence among urban primary care patients with diabetes. Methods: We randomly allocated 150 patients with diabetes to participate in a usual primary care visit either with or without the Statin Choice tool. Participants completed a questionnaire at baseline and telephone follow-up at 3 and 6 months. Results: Intervention patients were more likely to accurately perceive their underlying risk for a heart attack without taking a statin (OR: 1.9, CI: 1.0-3.8) and with taking a statin (OR: 1.4, CI: 0.7-2.8); a decline in risk overestimation among patients receiving the decision aid accounts for this finding. There was no difference in statin adherence at 3 or 6 months. Conclusion: A decision aid about using statins to reduce coronary risk among patients with diabetes improved risk communication, beliefs, and decisional conflict, but did not improve adherence to statins. Practice implications: Decision aid enhanced communication about the risks and benefits of statins improved patient risk perceptions but did not alter adherence among patients with diabetes. © 2009 Elsevier Ireland Ltd.