Seven patients with primary non-Hodgkin lymphoma of the skeleton were examined with MRI. The results were compared to "small cell" primary malignant bone tumors. The latter showed marked hyperintensity on SE T2-weighted images; in contrast, the lymphomas appeared as inhomogeneous lesions of low signal intensity on T2-weighted images. Histologic examination with silver stains of specimens of these lesions revealed a high content of fibrous tissue, which could explain the signal behavior on MR. All seven lymphomas were located in the epiphysis or metaphysis of the appendicular skeleton; intraarticular tumor growth was demonstrated in five cases.