A 61-year-old female presented with a 3-day history of painful and reddened right eye with painful ocular movements. She had been diagnosed as having systemic mastocytosis 4 years earlier. Ocular examination showed Best Corrected Visual acuity of 6/6 right eye and 6/6 left eye. There was marked conjunctival injection and chemosis. The posterior segment was normal. The left eye was normal. Exophthalmometry showed 2mm of right proptosis relative to the left eye. Computed tomography (CT) scans showed an ill-defined intra-conal lesion and enlargement of the lacrimal gland in the right orbit. A diagnostic biopsy was performed; the histopathology findings were of orbital mastocytosis. We present what our literature search suggests is the first biopsy-proven case of orbital mastocytosis.