The prevalence of JAK2V617F tyrosine kinase mutation differs between various variants of myelofibrosis with the higher detection rate for patients with post-polycythemia vera myelofibrosis (post-PV MF; 91%) if compared to primary myelofibrosis (PMF; 45%) and post-essential thrombocythemia myelofibrosis (post-ET MF; 39%). The impact of V617F point mutation and its allele burden on overall survival (OS) and the risk of leukemic transformation (LT) has been the subject of several studies, but the results were ambiguous. Our study included 77 patients with the following variants: 42 patients with PMF (55%), 16 with post-ET MF (21%) and 19 with post-PV MF (24%). Median age at diagnosis for the entire cohort was 61 years (range 19-81), with 53% of female. A total of 42 patients were JAK2V617F positive, giving an overall frequency of 55%; the median allele burden was 22% (range 2-96%). The JAK2V617F point mutation was detected in 21 patients with PMF (50%), 14 with post-PV MF (88%) and 7 with post-ET MF (37%). Lower JAK2V617F allele burden was more frequently detected in PMF patients, whereas higher allele burden was predominantly seen in post-PV/ET MF group. There was no significant difference between V617F-positive and V617F-negative patients in terms of studied parameters in PMF as well as in post-PV/ET MF subgroup. No significant difference was also demonstrated when the above-mentioned subpopulations were analyzed according to JAK2V617F allele burden, except higher leukocyte count in post-PV/ET MF patients with higher allele burden (14.3×10(9)/L vs. 6.2×10(9)/L; p=.03). Median follow-ups for V617F-positive and V617F-negative patients were 16.6 months (range 3.6-206.4) and 36.4 months (range 2.5-142.1), respectively. The presence of JAK2V617F mutation did not affect OS and the risk of LT development.