Introduction: Essential thrombocythemia is a Philadelphia chromosome-negative chronic myeloproliferative neoplasia with a risk of bleeding and thromboembolic complications during the course of illness. Cytoreductive drugs, such as non-selective hydroxyurea or interferon as first-line and specific, megakaryocyte-thrombocyte reductive anagrelide chosen as second-line treatment in cases of adverse, intolerable effects of hydroxyurea can lower the incidence of bleeding/thrombotic episodes in patients with essential thrombocythemia. Aim: In this observational survey the effect of anagrelide was investigated in patients with essential thrombocythemia, who were first treated with hydroxyurea but failed to have clinicopathologic reponse (resistant) or were intolerant (adverse effects). Method: Between 2000 and 2014, 104 patients were diagnosed with essential thrombocythemia and treated first-line with hydroxyurea (weekly median dose of 7500 mg) in the haematologic outpatient department of the authors. Because of intolerance and/or resistance, hydroxyurea was changed to anagrelide (7.5 mg weekly median dose), the doses of hydroxyurea and anagrelide were adjusted to achieve clinicopathological response according to the updated criteria of the European LeukemiaNET. Effect of anagrelide as monotherapy (first-or second-line after hydroxyurea) or in combination with hydroxyurea was followed. Statistical analysis was performed using the Windows Statistical Package Program. Results: Of the 104 patients with essential thrombocythemia (according to the updated WHO-ET classifications 58 patients JAK2V617F mutation positive, 46 patients negative, 15 patients calreticulin mutation negative, 6 patients MPL-1 mutation negative) 87 patients received hydroxyurea in first line, 4 patients interferon, and 13 patients acetylsalycilic acid only. Seven patients who proved to be intolerant and 22 patients who were resistant to hydroxyurea received anagrelide in second line (in 18 patients monotherapy and in 11 patients in combination with hydroxyurea), while other 5 rather young patients in first line therapy (34/104, 32.6%). In the anagrelide first line group 5 patients (100%), in the second line anagrelide monotherapy group 16 patients (88,8%), and in the combined hydroxyurea plus anagrelide group 9 patients (82.1%) achieved complete remission. The 10-year overall survival was 82.1%. In 2 patients treated with anagrelide major bleeding and in one patient myocardial infarction occurred, other serious adverse events due to anagrelide treatment were not detected. Three elder patients died from non-hematologic diseases, but leukaemic transformation was not observed. Conclusions: First or second line anagrelide therapy, combined with hydroxyurea if necessary, was able to reduce the platelet-count and the rate of complications, and to control the course of essential thrombocythemia with tolerable adverse effects.