This report describes a unique case of acute promyelocytic leukemia (APL) showing elusive morphologic features, an atypical pattern of cytochemical reactions, and a previously unreported immunophenotype consistent with a very early myeloid form: CD13 (+), CD33 (+), CD9 (+), CD2 (+), HLA-DR (-), CD34 (+), CD117 (+), and TdT (+). The diagnosis of AML M3 variant was made only after genotypic analyses revealed the PML/RAR alpha rearrangement associated with the typical (15;17) (q22;q21) translocation. This example of 'asynchronous differentiation' emphasizes the need for a multiparameter approach to the diagnosis of acute leukemia.