Objective:We aimed to investigate the frequency of Janus kinase 2 (JAK2) mutations in cases with chronic myeloproliferative disorders (CMDs), and the relationship between the presence of JAK2 mutation and leukocytosis and splenomegaly, retrospectively.Materials and Methods:Patients, who were diagnosed with BCR-ABL-negative CMDs according to diagnosis criteria of the World Health Organization and followed up at the hematology clinic between 2013 and 2015, were investigated in terms of the frequency of JAK2 mutation in cases with CMDs, and the relationship between the presence of JAK2 mutation and leukocytosis and splenomegaly, retrospectively.Results:In total, 100 patients, who were diagnosed with BCR-ABL-negative CMDs, were evaluated retrospectively. The mean age of the patients with JAK2 positivity was significantly higher compared to patients with negative. JAK2-positivity rates in the age groups were significantly different. Gender, diagnosis, splenomegaly, and leukocytosis were not statistically different for JAK2 positivity between the groups.Conclusion:JAK2 V617F mutation is more commonly seen in older age as a risk for complications related to CDMS. Splenomegaly and leukocytosis are not associated with JAK2 V617F mutation.