We present a case of a 75-year-old woman with right mandible cystic lesion and primary hyperparathyroidism. The MRI demonstrated marked loss of signal intensity on T2 gradient-echo images, suggesting intralesional hemossiderin. After an open biopsy, histology was consistent with "brown tumor." The finding of susceptibility on T2 gradient-echo images in a mandible lesion adds considerable specificity to the differential diagnosis.