Cutaneous plasmacytoma is an uncommon observation in clinical practice. It is usually a consequence of direct extension from an underlying bony lesion, in the setting of multiple myeloma. In our case, a 77-year-old woman, with stage IIIA IgG lambda multiple myeloma for two years, presented with firm nodular violaceous cutaneous lesions on the left arm without underlying bone osteolytic lesions or subcutaneous tumors; the biopsy was consistent with plasmacytoma. The patient had suffered two spontaneous left humeral fractures treated with prosthesis replacement just before the initial diagnosis of multiple myeloma. She had also been submitted to radiotherapy for a subcutaneous plasmacytoma, detected some months before, at the same site of the cutaneous lesions. Despite optimal response of the cutaneous lesions to treatment, the disease progressed and the patient died from infectious complications eight months after the appearance of the tumors.