In a group of 36 Mexican mestizo patients with MPN, we studied five molecular markers: The BCR/ABL1 fusion gene, the JAK2 V617F mutation, the JAK2 exon 12 mutations, the MPL W515L mutation and the MPL W515K mutation; 17 patients with essential thrombocythemia (ET), eight with polycythemia vera (PV), four with primary mielofibrosis (MF), five with undifferentiated MPN, one with primary erythrocytosis and one with familial thrombocytosis.