Paraneoplastic limbic encephalitis is a rare disorder that has been previously diagnosed on clinical and pathologic grounds without good radiologic correlation. We present the case of a 42-year-old woman who developed gradually progressive limbic dysfunction 4 years after undergoing mastectomy for breast cancer. Although CT scans were normal, magnetic resonance (MR) imaging showed signal abnormalities in the medial portions of both temporal lobes, the amygdaloid nuclei, and the hypothalamus. An MR-guided temporal lobe biopsy confirmed the presence of encephalitis.