history of hypertension. She took irbesartan 150 mg once daily, diltiazem 90 mg twice daily, and aspirin 100 mg once daily. Her electrocardiography and echocardiography were normal. Myocardial perfusion scintigraphy revealed inferior hypoperfusion suggestive of ischemia. We planned multislice coronary computed tomography because of the patient refused the coronary angiography. Significant circumflex coronary artery lesion (70%) was found at tomography. We planned percutaneous transluminal coronary angioplasty and stent implantation of the circumflex coronary artery after 2 weeks. She was prescribed clopidogrel which is irreversibly inhibiting P2Y12 and adenosine diphosphate receptor on platelet cell membranes 75 mg once daily(1). One weeks later she presented to our hospital with severe pain of his left knee. The knee was tender and hot. His erythrocyte sedimentation rate (42 mm/hour) and C-reactive protein (17 mg/dL) were increased. Other hematological, biochemical and rheumatological findings such as glucose, urea, creatinin, uric acide, sodium, potassium, calcium, thyroid function tests, romatoid factor, and antinuclear antibody were normal. Knee X ray films and magnetic resonance imaging showed signs of soft tissue swelling. Clopidogrel was discontinued. One week later the joint pain and inflammatory tests had improved. After recovery, clopidogrel 75 mg/day was re-initiated, but the same complaints were re-induced. The patient refused the percutaneous intervention and medical therapy without clopidogrel was started. Finally, according to this findings, clopidogrel may be a cause of acute arthritis(2)