We report a case of Lymphocytic Lymphoma presenting with primary manifestation in the prostate. A 82 year-old man presented to emergency department with acute urinary retention. Digital rectal examination revealed a voluminous and firm prostate. Histology confirmed involvement of the prostate by small B Lymphocytic Lymphoma. The patient was treated with chlorambucil. Lymphocytic infiltration of prostate is a rare manifestation. However this may also be the first sign of an undiagnosed lymphoma. This observation shows that the prostatic lymphoma must be considered among the causes of low urinary retention.