We report a case of a brown tumor with fluid-fluid levels in a patient with primary hyperparathyroidism. A 19-year-old woman presented with a 3-month history of pain in the left pubic region. The laboratory data showed elevated serum calcium and intact parathyroid hormone, confirming the diagnosis of primary hyperparathyroidism. Plain radiography and computed tomography (CT) showed an expansile lytic lesion of the superior ramus of the left pubis. The cortex was thinned. On magnetic resonance (MR) images, the lesion was solid and cystic. The solid area of the lesion showed heterogeneous low to intermediate signal intensity on T1-weighted images and heterogeneous low to high signal intensity on T2-weighted images. The cystic area showed several fluid-fluid levels on T2-weighted images. Dynamic contrast-enhanced MR images after administration of Gd-DTPA showed marked, early enhancement of the solid area of the lesion. A delayed image showed prolonged enhancement of the solid area and enhancement of the septa and walls of the cystic area. Histopathology of a biopsy specimen showed fibroblastic proliferation, abundant giant cells, and focal hemosiderin deposition, which supported the diagnosis of a brown tumor. After removing the parathyroid adenoma, the brown tumor regressed and became sclerotic on radiographs.