This report describes the case of a 48-year-old woman found to have a leiomyoma of the left adrenal gland after presenting with anemia and hypertension. An upper gastrointestinal series revealed a mass in the posterior region of the body that distorted the stomach. A computed tomography (CT) scan showed a well-circumscribed mass with a high-density outline in the left adrenal gland, and magnetic resonance imaging (MRI) revealed a homogeneous mass. Multiple catheter samplings of vena cava blood revealed a slight elevation of epinephrine and norepinephrine in the left adrenal vein and the left renal vein. Thus, asymptomatic pheochromocytoma of the left adrenal gland was highly suspected as a preoperative diagnosis and a left adrenalectomy was performed. However, histologic examination subsequently revealed findings suggestive of leiomyoma of the adrenal gland, which was confirmed by electron microscopy. The patient's postoperative course was uneventful and she has remained free from any further symptoms.