Orbital involvement in multiple myeloma is unusual. We describe the case of a 60-year-old male who presented with left proptosis, reduced visual acuity, diplopia and progressing signs of globe indentation 2 months after chemotherapy for multiple myeloma. MRI showed a well-defined tumor filling the mediobasal part of the left orbit. Incisional biopsy and reduction of tumor mass were performed using an anterior transconjunctival orbitotomy. Histopathologic findings and further systemic examination confirmed the reactivation of the multiple myeloma. Proptosis, intraocular pressure and visual acuity improved following external beam radiation therapy of the left orbit and repeated systemic chemotherapy. Orbital involvement in multiple myeloma was the only sign of insufficient chemotherapy.