A primary leiomyosarcoma of the right adrenal gland is reported in a 49-year-old male who presented with progressive flank pain. This is the second case in the English language literature and the first to have documentation of malignant behavior. The tumor measured 11 cm in diameter and showed marked necrosis with prominent mitotic activity (average 15 per 10 high-power fields). Smooth muscle differentiation was apparent ultrastructurally and confirmed by positive immunostaining for muscle-specific and alpha-smooth muscle actin. Bony metastases developed; following palliative treatment with radiation and chemotherapy, the patient is alive with tumor 9 months later. Origin from smooth muscle associated with the central adrenal vein or its tributaries is proposed.