A 59-year-old man presented with a painless testicular mass and underwent a radical orchiectomy. The resected specimen showed a 5-cm-sized, white-yellow and homogenous solid mass in the testicular parenchyma. Histologically, the central part of the tumor exhibited typical features of seminoma. The peripheral part of the tumor exhibited diffuse infiltration of small, monotonous lymphoid cells involving the tunica albuginea. The monotonous lymphoid cells were immunoreactive for CD20, CD79a, CD5, and CD23, and negative for CD3, CD10, and cyclin D1. Kappa light chain restriction was detected on flow cytometry using the resected specimen. Considering the circulating lymphoid cell count of >5.0×103/µL, we diagnosed the peripheral component of the tumor as an infiltration of chronic lymphocytic leukemia. This extremely rare combination of seminoma and lymphoid neoplasm should be considered in the differential diagnosis of classic seminoma with extensive lymphoid reaction in tumors arising in elderly patients.