The authors review the radiologic spectrum of fat-containing soft-tissue masses of the extremities, with emphasis on computed tomography, magnetic resonance imaging, and pathologic correlation. These masses include both common and uncommon, benign and malignant lesions, such as lipoma, intramuscular and intermuscular lipoma, neural fibrolipoma, lipoblastoma, lipomatosis, hibernoma, hemangioma, elastofibroma, and liposarcoma, as well as lesions that may mimic fat-containing soft-tissue masses. Imaging studies of fat-containing lesions will often allow a specific presumptive diagnosis. When a specific diagnosis is not possible, however, knowledge of the spectrum of fat-containing lesions will allow a suitably ordered differential diagnosis.