Among primary malignant prostatic tumors, those of lymphoid origin are considered to be extremely rare. To date, however, a fair number of cases of so-called primary lymphosarcoma of the prostate gland have been reported, but the great majority of them have been discarded by recent investigators on the ground that insufficient clinical or histologic evidence was presented to justify the diagnosis. Since carcinoma is the most frequent type of primary malignant tumor of the prostate gland and since many of these prostatic new growths may be composed of primitive, highly undifferentiated cells, a majority of the tumors reported as lymphosarcoma have been looked on as highly anaplastic carcinoma which was called lymphosarcoma by mistake. A strong point in favor of the rarity of lymphosarcoma in this organ is the absolute paucity, not to say absence, of lymphoid tissue from which primary lymphosarcoma could arise. We shall come back to this