To investigate the pattern and dimension of cortical bone abnormality on magnetic resonance imaging (MRI) as a feature to distinguish primary lymphoma of bone from osteosarcoma and Ewing sarcoma, 46 patients with primary malignant bone lesions with a soft tissue mass (16 osteosarcomas, 15 Ewing sarcomas, 15 lymphomas) were examined with MRI (T1-weighted pre-/postcontrast spinecho sequences and T2-weighted spin-echo and fast spinecho sequences; 1.5 T system). Qualitative image analysis revealed no differences for signal characteristics and enhancement. Lymphomas appeared significantly more often homogeneous (47%; Ewing sarcoma 20%; osteosarcoma 6%), and patients were significantly older (cutoff point 30 years). Lymphomas showed significantly less frequent cortical abnormality (60%; Ewing sarcoma 87%; osteosarcoma 100%), complete penetration (13%; Ewing sarcoma 67%; osteosarcoma 87%), focal destruction (13%; Ewing sarcoma 40%; osteosarcoma 81%), and complete destruction (0%; Ewing sarcoma 13%; osteosarcoma 19%). In conclusion, primary lymphoma of bone is characterized by minimal cortical changes despite an accompanying soft tissue mass in a patient over 30 years of age. J. Magn.