The primary clear cell tumor of the lung is an extremely rare benign tumor. This tumor is called "sugar tumor" since clear cell tumor of the lung contains abundant glycogen. We here present a case of lung clear cell tumor of the lung associated to essential thrombocythemia. To the best of our knowledge, there is no report about this association. A 44-Year-Old Woman admitted to our clinic with a 2-month history of fatigue. On physical examination, the spleen was 3 cm palpable below the left costal margin on the mid axillary line. The laboratory tests revealed an elevated platelet counts (1,014,000/mm(3)). A pulmonary nodule (3,5 cm) was detected in the upper right lobe on the chest X-ray. Then, thoracic computed tomography (CT) was planned. The nodule looked like benign pattern on CT scan and total excision was performed for curative and diagnostic treatment. Microscopically, the tumor was composed of nests of rounded or oval cells with distinct cell borders, optically clear cytoplasm and small nucleus. By immunohistochemistry, tumor cells were positive for HMB-45, NSE and focal S100 antigen. And, it was diagnosed as clear "sugar" cell tumor. After tumor excision the lasting thrombocytosis induced us to perform bone marrow biopsy and JAK2 mutation research. Diagnosis of Essential Thrombocythemia was made. In conclusion, it is important to make an evaluation for myeloproliferative diseases in clear "sugar" cell tumor in adults if thrombocytosis was lasting after treatment.