Introduction: Up to 50% of chest wall tumors are malignant; among which rib plasmocytoma stand out. Aim: Showcase a clinical case that debuted as a rib plasmacytoma, and that ended up presenting as Multiple Myeloma. Materials and Method: Records of a patient with resection of chest wall tumor. Results: Male patient of 58 years, with one year of costal pain, associated with an indurated increase in volume at the level of the eighth right rib in the mid-axillary line. Chest CT scan demonstrated a suggestive image of plasmacytoma of 79 x 44 mm. Surgical resection was performed, with prolene mesh installation in the defect. Biopsy showed neoplastic compromise due to monoclonal lesion of plasma cells. Study is com-plemented with bone marrow biopsy confirming multiple myeloma. The patient was treated with adjuvant chemotherapy. Conclusions: Solitary bone plasmacytoma is a low frequency entity, which is associated with the presence of multiple myeloma. At the moment of suspicion, it is necessary to rule out their pre-sence, in order to improve the patient’s prognosis.