Objective: To emphasize that solitary orbital extramedullary plasmacytoma, a rare tumor, is not invariably radiosensitive.

Methods: We examined a patient who had undergone empirical irradiation that failed to control an orbital tumor.

Results: After a second biopsy had secured the diagnosis of a solitary extramedullary plasmacytoma, further irradiation proved ineffective and exenteration was required. The patient was free of recurrence one year after exenteration and had satisfactory cosmesis with a prosthesis.

Conclusions: A histologic diagnosis is essential before treatment is commenced so that the correct radiation dosage is used.