Some AML groups, namely t(15;17), t(8;21) and FAB M7, more frequent in children than adults, were clearly distinguished whereas AML with CBFB/MYH11 fusion gene (inv(16)) and KMT2A chimeric fusion genes revealed more heterogeneity, indicating the existence of additional subgroups. The gene discussed is CBFB; the disease is acute myeloid leukemia.