The molecular pathogenesis underlying the primary myelofibrosis (PMF) progression to acute myeloid leukemia (AML) is still not well defined. The involvement of microRNA (miRNA) is actually helping to shed light on an important issue in the occurrence of myeloproliferative neoplasms (MPNs). However, the role of intronic miRNA, derived from the intron regions of gene transcripts, has never been reported in MPNs. In this study, we describe a PMF case evolved to AML with a t(12;18)(p13;q12) rearrangement showing the downregulation of the intronic miR_4319 and the overexpression of its host gene, SET binding protein (SETBP1). A possible molecular mechanism regulating the PMF progression to AML is discussed.