Essential thrombocythemia (ET) is a rare myeloproliferative disorder occurring predominantly in the elderly population. Its occurence in the pediatric age group is even more rare. We report a 13-year-old girl who presented with isolated cerebral venous thrombosis and was diagnosed with essential thrombocythemia. family screening for any thrombocytosis was 20 negative. With no secondary cause apparent for persistent thrombocytosis, we looked for the JAK2 mutation, but the result was negative. in contrast to linkage of JAK2 mutation positivity with increased thrombotic risk, our case showed that thrombosis can occur in the absence of JAK2 mutation in a case of essential thrombocythemia. the indications for treatment and the best treatment of children with ET are currently not known, and guidelines for the management of children with ET are needed. Adult patients have near-normal life expectancy because of the low rate of leukemic conversion, but no child has been monitored long enough to assess prognosis.