The JAK2(V617F) mutation occurs in 50% of patients with essential thrombocythemia (ET). We investigated the correlation between the JAK2(V617F) mutation and clinical and laboratory characteristics, thrombohemorrhagic risk and incidence of disease evolution in 275 patients with ET followed for a median follow-up of 7 years. JAK2(V617F) mutation was detected in 175 patients (64%), of whom 173 were heterozygous. Patients with the mutation were older and displayed higher hemoglobin and hematocrit levels, but lower platelet count. Cytotoxic treatment requirement was similar in the two groups, but patients with the mutation showed better responses. Incidence of thrombosis and disease evolution was comparable. JAK2 mutational status assessment was valuable to distinguish two populations of patients with ET, showing distinctive hematologic and clinical features.