Anaplastic gangliogliomas (AGGs), the malignant counterpart of gangliogliomas, are classified as grade III tumors by the World Health Organization. Although, the clinical course and optimal treatment of AGGs are not well understood, they often result in worse local control rate and shorter survival. The authors describe the magnetic resonance imaging findings of a middle-aged woman with supratentorial AGG, that manifested as a rapidly growing cystic mass which mimicked metastasis. The authors suggest that AGG may be considered as a possible diagnosis for a rapidly growing peripheral enhancing mass in the brain, especially when it is superficially located.