Essential thrombocythemia is a disorder that causes persistent increase in the platelet count. The disease is associated with an elevated risk of thrombosis. A 71-year-old woman was diagnosed with left main coronary thrombosis after an angiogram due to stable angina. One week before the angiogram was taken the patient had also been diagnosed with essential thrombocythemia. After appropriate medical treatment for 5 days the patient underwent an excimer laser treatment, which failed in dissolving the thrombus. Before the patient underwent coronary surgery, thrombopheresis was performed in order to reduce the platelet count. After a successful coronary operation the patient improved completely.