This case report describes a rare case of testicular metastasis from renal cell carcinoma, which led to first diagnosis of the primary. The patient presented with a progressive painless swelling of the left testicle. After initial suspicion of a testicular tumor, inguinal excision of the testis was performed, which confirmed the presence of a clear cell carcinoma. Further investigations revealed evidence of a primary carcinoma on the left-lower pole of the kidney, which was removed by partial nephrectomy. Histopathologically, clear cell renal cell carcinoma was confirmed. Treatment was supplemented by adjuvant immunotherapy with pembrolizumab. Postoperative follow-up has shown no evidence of recurrence to date.