The testicular plasmocytoma represents only 5% of the non-germinative cell testicular tumors, and accounts for only 2% of all plasma cell neoplasms. Approximately, 50 cases of testicular plasmocytoma have been reported in medical literature; however, only 9 of these are isolated tumors without previous history or progression to multiple myeloma. A 47-year-old patient, presenting progressive and painless growth of the right testicle in the last four years, underwent surgical treatment in another hospital two years ago, to correct a hydrocele in the same testicle with no improvement at all. Sonography showed a tumor with the following measurements for the right testicle: 84 × 59 × 80 mm. The tumor marker values were all normal. An abdominal computed tomography found no evidence of retroperitoneal lymph nodes invasion. The patient underwent a right radical orchiectomy. Pathologic analysis revealed a malignant neoplasia described as a plasmocytoma (solitary myeloma) that produces immunoglobulin's kappa light chain. After five years of follow-up, there were no signs of metastasis or local recurrence in the exams. Case report and review of literature have been presented here.