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Fibrous histiocytomas (FHs) involving the orbit are uncommon. To our knowledge, here the authors report the first patient with an orbital low-grade malignant FH originating from the medial rectus muscle.A clinical report relating clinical features as well as imaging and histopathologic findings is presented.A 26-year-old female presented with a left eye proptosis that had been present for 4 months. A small left exotropia was observed and ocular motility evaluation revealed a −3 adduction and −1 abduction of the left eye. B-mode ultrasonic scans demonstrated a 2.5 × 2.0 cm mass with medium internal echo and a clear boundary located in the nasal region of the left orbit. Magnetic resonance imaging (MRI) showed a 2.8 × 2.0 cm oval extraconal orbital mass, with isointensity on T1-weighted MRI and hyperintensity on T2-weighted MRI. An anterior orbitotomy was performed and the tumor was completely removed. The mass originated from the medial rectus muscle. Histopathologic evaluation confirmed a low-grade malignant FH. After surgery, the left exotropia was no longer present. Ocular motility revealed a −1 adduction and −1 abduction of the left eye. No recurrence was evident at 1 year after surgery.This rare patient demonstrates that FH may originate from the medial rectus muscle. With careful surgical dissection, a near normal function of the involved muscle can be restored.