This study was undertaken in order to examine both the prevalence and the associated clinicopathologic and genetic features of FIP1L1-PDGFRA rearrangement in a cohort of 15 adult patients presenting with eosinophilia and an absolute eosinophil count higher than 1.5 × 109/L. The gene discussed is PDGFRA; the disease is Increased total eosinophil count.