Introduction: Testicular tumor is one of the rarest tumors that accounts for 1-2% of male tumors and 95% of them are germ cells. The present study reported a case of scrotum mass, the first clinical manifestation of multiple myeloma. Case Report: The patient was a 48-year-old man with a large mass without pain in the left scrotum and referred to a urology clinic. There was no bone pain, lethargy, or weakness on clinical examination. Vital signs, heart, lung, and abdominal examinations were all normal. Ultrasound showed a large 10-cm-diameter Izuaco mass in the left hemiscrotum with inflammation and edema of the scrotum wall. With the diagnosis of a left testicular tumor, the decision was made to perform surgery. On the fourth day after the operation, the patient developed a large hematoma in the left hemiscrotum, which was operated on again and the hematoma was drained. In the experiments, a decrease in blood hemoglobin of up to 6. 5 and a decrease in platelets of up to 32, 000 and an increase in blood creatinine were observed. Simultaneously with supportive therapies to correct anemia and platelets and the necessary measures to correct renal function, which was also effective due to high ESR and total protein, a cranial X-ray was taken, which contained lytic lesions. With a high suspicion of multiple myeloma, he was consulted by a respected internal medicine specialist. Conclusion: In this patient, coagulation disorder and subsequent mild trauma to the testicle, which the patient does not remember, may have caused bleeding in the testicle and a mass in it. Of course, the presence of anemia should suggest other differential diagnoses. However, the lack of tumor reporting in the sample sent to the laboratory necessitates further investigation. Recurrent hematoma at the site of surgery in this patient and the impossibility of determining blood type raised the suspicion of high proteins in the blood, which together with high ESR serum despite the relatively young age of the patient led us to the diagnosis of multiple myeloma.