Twenty-two patients with clinical presentations of either orbital lymphoma or orbital inflammatory syndrome (OIS) involving 25 orbits were examined by magnetic resonance imaging (MRI) before biopsy. To determine whether MRI adds specificity to radiographic diagnosis, the MRI signal characteristics of all tumors were examined. Attention was focused on the signal intensity of each tumor on T1- and T2-weighted images. In nine of 12 (75%) orbital lymphomas, the tumors appeared hyperintense to fat on T2-weighted images and became brighter relative to their appearance on T1-weighted images. In 11 of 13 (85%) orbital infiltrates with OIS, the tumors appeared isointense to fat on T2-weighted images and became slightly darker or unchanged relative to their appearance on T1-weighted images. Tumor density and homogeneity were fairly similar in all 25 lesions and were therefore not useful for further differentiation. Similarly, the presence of moderate enhancement with gadopentetate dimeglumine was seen in all but one tumor, and it was therefore not useful for further differentiation.