The adrenal gland receives its arterial supply from multiple small branches of the inferior phrenics, aorta and renal arteries. The venous drainage is into a single large vein on each side, the left draining into the renal, the right into the inferior vena cava. There may be additional small venous communications, patricularly to renal capsular veins. The latter continue to drain adrenal hormones even after main adrenal vein ligation and must be taken into account when operating for pheochormocytoma.