We describe a rare case of isolated extraocular muscle ocular adnexal lymphoma of a middle-aged female who presented with redness in the left eye associated with progressive proptosis over one year. Magnetic resonance imaging of the orbit indicated isolated enlargement of the left superior oblique (SO) muscle with an apparent diffusion coefficient (ADC) of (0.77 ± 0.11 × 10-3 mm2/s). Histopathology with immunohistochemical staining of the incisional biopsy from the SO muscle belly confirmed the diagnosis of extranodal marginal zone B cell lymphoma.