A case of trisomy 13 is presented: a 73-year-old man with acute nonlymphocytic leukemia (ANLL), FAB borderline M1/M2, and peripheral leukocyte and platelet counts that were difficult to control with chemotherapy. A literature review shows that 35 cases of trisomy 13 are known at present. They are characterized by male predominance (76%), preferentially myeloid disorders (ANLL, myelodysplastic syndromes, chronic myeloid leukemia), leucocytosis, and relatively high platelet counts and hemoglobins. It is suggested that trisomy 13 is a specific nosologic entity with male predominance and characterized by interference with proliferation and differentiation in the myeloid differentiation series.