Plasmacytomas occur in bone marrow or in extramedullary sites, typically in the head and neck. Intramuscular plasmacytoma is rare and reported occurring in the orbits and upper limbs. We report a rare case of intramuscular extramedullary plasmacytoma (EMP) occurring in the gluteus medius muscle. In this case, an elderly lady with known multiple myeloma, presented with a lump in her right buttock. Subsequent imaging demonstrated a non-specific intramuscular mass in the right gluteus medius. Treatment is traditionally surgical resection plus/or adjuvant chemotherapy or autologous stem cell transplant. Plasmacytoma was considered among the differentials, despite the non-specific imaging features, and atypical location. It allowed for a rapid multidisciplinary team discussion about the risks and benefits of a biopsy. Unfortunately, the patient died before treatment could be started. The purpose of this report is to remind clinicians to include plasmacytoma as a differential for soft tissue masses, even in atypical locations. We also discuss the relevant imaging features and management of EMPs.