IgG4-related disease is an emerging disease entity characterized by elevated serum IgG4 concentration and tumefaction or tissue infiltration by IgG4-positive plasma cells. In IgG4-related disease, tumor-like lesions develop in multiple organs, such as the lacrimal gland, salivary gland, lung, pancreas, kidney, and lymph nodes. We report here three cases of IgG4-related orbital inflammation that presented as unilateral pseudotumors. The patients all were men, with an age range of 65-75 years. The patients had been pointed out unilateral intra-orbital masses, and histopathological examinations revealed marked accumulation of IgG4-positive plasma cells (IgG4/IgG ratio: 51.1-71.6%) with fibrosis. But storiform fibrosis was seen in only one case, and no obliterative phlebitis was seen. The serum levels of IgG4 were increased to 178-670 mg/dL. The masses had well-defined homogeneous signal intensities, and they were hypo-intense on T1-weighted MR images and iso-intense on T2-weighted MR images. Gadolinium enhanced mass lesions in two cases. All orbital mass lesions responded well to corticosteroid treatment.