OBJECTIVE To report a case of increased international normalized ratio (INR) in a geriatric patient receiving warfarin and ropinirole. METHODS A 63-year-old African-American man with a history of Parkinson disease, Alzheimer disease, and status post-cardio-vascular accident was evaluated for symptoms of progressing stiffness and rigidity. Ropinirole was added to his current therapy for Parkinson disease, with a corresponding decrease in the dose of levodopa/carbidopa to allow levodopa sparing. On laboratory evaluation, he was noted to have an increased INR nine days after these adjustments; the INR had previously been stable. No other significant medication, social, or diet changes were noted. Warfarin was withheld for four days and restarted at approximately 75% of the previous weekly dose. The patient had no obvious signs of bleeding. Furthermore, the warfarin dose was again increased after discontinuation of ropinirole due to common gastrointestinal adverse effects. CONCLUSIONS Warfarin is an oral anticoagulant whose narrow therapeutic index and potential for drug interaction is well documented. It is always possible that a change in blood coagulability can occur without an obvious contributable cause; however, an acute change in a previously stable INR with the addition of other medications always raises questions as to the possible mechanism of adverse reaction. No previously documented interaction of this precise nature has been identified. CONCLUSIONS Ropinirole may elevate the anticoagulant effects of warfarin. Patients receiving warfarin should be considered for more frequent INR monitoring when ropinirole is added, adjusted, or discontinued from their medical regimen.