Leiomyosarcoma of the adrenal gland is extremely rare in the literature. We present a patient with an adrenal leiomyosarcoma originating from the adrenal vein, the pathologic findings and management. A 66-year-old man who was a hepatitis B virus carrier was found to have a huge left suprarenal mass on sonography and computed axial tomography. A huge tumor in the left suprarenal area with a markedly engorged adrenal vein was found during an adrenalectomy. The tumor thrombus extended into the renal vein, close to the inferior vena cava. The left adrenal gland with the whole tumor thrombus was removed completely. Microscopically, the adrenal gland was compressed but not invaded by the spindle cell tumor, which was composed of interlacing fascicles of neoplastic smooth muscle cells. The tumor was localized within the adrenal vein and arose from the venous wall. The patient had no local recurrence for 18 months after en bloc excision of the tumor. We suggest that en bloc excision with a clear and adequate surgical margin is the most important cure procedure for adrenal leiomyosarcoma.