The authors present a rare case of plasmacytoma of the orbit involving lacrimal gland with secondary transformation into multiple myeloma in a 42-year-old woman. The lesion was surgically removed and analyzed. Histopathological examination with immunostaining revealed it to be positive for immunoglobulin G and Kappa chains, demonstrating monoclonality. However, no abnormality was observed on serum electrophoresis, skeletal survey and bone marrow aspiration. Therefore, the tumor was diagnosed solitary plasmacytoma of bone. The patient was treated with external beam radiotherapy and has remained disease free for 5 years and 6 months until 2007, when she presented a pathological fracture due to multiple myeloma. Extensive medical work-up to rule out multiple myeloma or other malignant lymphoproliferative conditions involving orbit or ocular adnexa is needed when the diagnosis of solitary plasmacytoma of bone is suspected because treatment and prognosis are very different.