Chromosomal translocations involving the platelet-derived growth factor receptor beta gene (PDGFRB) have been reported in a subset of patients with atypical myeloproliferative disorders (MPDs). The fusion of the PDGFRB gene, which encodes a tyrosine kinase receptor, with different partner genes results in its constitutive activation. We present the cases of two patients with atypical MPD carrying t(4;5)(q21;q33) and t(2;5)(p21;q33), respectively. Fluorescence in situ hybridization demonstrated that PDGFRB was involved in both translocations. Further characterization of the 4q21 breakpoint using a bacterial artificial chromosome probe revealed PRKG2 as the likely gene partner to PDGFRB. Characterization of the 2p21 breakpoint identified a novel gene partner to PDGFRB, the SPTBN1 gene. Both patients achieved a complete molecular remission after introduction of imatinib mesylate therapy.