A 76-year-old woman presented to a clinic with fever and loss of body weight. Abdominal echogram showed bilateral adrenal swelling (left adrenal 90x80 mm, right adrenal 50x20 mm) and she was admitted to the hospital for further examination. A tumor was also found inside nasal cavity by enhanced computed tomography (CT), and abnormal uptake in the nasal cavity and adrenal gland was shown in gallium scintigraphy. Laboratory tests revealed the elevation of lactate dehydrogenase (LDH) and sIL-2R. Biopsy of the nasal tumor revealed nasal natural killer or thymus-derived (NK/T) cell lymphoma. No Epstein-Barr virus (EBV) -encoded RNA was detected in tissue. After THP-COP chemotherapy regimen, both the nasal and adrenal tumors decreased in size. However, a CT scan taken on admission revealed a pulmonary embolism. After treatment with heparin and warfarin, emboli disappeared. Chemotherapy was continued, but perforation of the small intestine occurred. Since the prognosis was poor, no operation was performed. Her condition slowly, and she died 60 days after admission. Since she had a high level of plasma ACTH (158.0 pg/ml) and normal serum cortisol (14.6 microg/dl), partial adrenal insufficiency was suspected. In addition, since her cortisol circadian rhythm was lost and cortisol levels were not completely suppressed by the 1 mg and 8 mg dexamethasone test, she met the criteria of the diagnosis of preclinical Cushing syndrome. NK/T cell lymphoma with giant adrenal tumor is extremely rare, but should be considered as one of the differential diagnoses of bilateral adrenal tumor.