A 51-year-old man without human immunodeficiency virus, hepatitis B virus or hepatitis C virus was admitted with left scrotum swelling and hydrocele. The cytological finding of fluid in the left scrotum revealed malignant lymphoma, and the immunophenotypic analysis and monoclonal rearrangement of immunoglobulin heavy chain demonstrated B-cell lymphoma. However, no solid tumor of lymphoma was identified in the specimen following a left orchiectomy, or in any other body site and genomic human herpes virus-8 and Epstein-Barr virus were not detected in the lymphoma cells. So we interpreted this as a primary effusion lymphoma without any ethological viral infection. Subsequently, he underwent chemo-radiation therapy and has remained in remission.