Prolymphocytic leukemia is an entity characterized by morphologic, immunologic, clinical and behavioral features which allows its keeping apart from chronic lymphoid leukemia. Careful analysis of blood smear is the main step for its diagnosis. Our purpose is to remind this particular chronic lymphoproliferative syndrome which requires energetic initial treatment. Prolymphocytic leukemia de novo as well as a possible transformation of chronic lymphoid leukemia to prolymphocytic leukemia are discussed.