Essential thrombocythemia (ET) is usually managed by anti-platelet therapy. European guidelines recommend that patients with ET at high risk of developing thrombohemorrhagic events should be placed on cytoreductive therapy (CRT). In Japan, hydroxycarbamide (HC) is the most widely used CRT; however, treatment options for patients who become intolerant or refractory to initial treatment are limited. This study sought to determine the efficacy, safety, and tolerability of anagrelide in high-risk Japanese adults with ET who were intolerant or refractory to their first-line CRT. Fifty-three patients were enrolled in the study. Of those, 67.9 % had a platelet response (<60 × 10(4)/µL) and 45.3 % achieved normalization of platelet counts (≤40 × 10(4)/µL) on anagrelide therapy. The median time to platelet count response was 98.5 days and the median time to platelet count normalization was 274.0 days. The median daily dose administered was 1.9 mg/day. The most common adverse events observed during anagrelide treatment were anemia, headache, palpitations, and diarrhea. The majority of these were either mild or moderate in severity. Overall, the safety profile of anagrelide in high-risk Japanese patients with ET was consistent with the European Summary of Product Characteristics.