Waldenström's macroglobulinemia is a rare disease with an indolent clinical course. The median age of the affected patient is 65 years. Nevertheless, we report a case of Waldenström's macroglobulinemia revealed by a splenomegaly and severe pancytopenia, in a 51-year-old man without previous medical history. According to the recent consensus recommendations for the clinicopathological definition of Waldenström's macroglobulinemia, diagnosis was made through morphological and immunophenotypic data of medullary cells. The reduced survival of the patient is associated with the importance of the cytopenia.