INTRODUCTION: Therapeutic thrombocytapheresis (TTA) is used to promptly reduce platelet count to prevent thrombohemorrhagic complications that may develop in extreme thrombocytosis. In this study, the efficacy and safety of TTA were investigated in our patients who underwent TTA for extreme thrombocytosis for more than 20 years. MATERIALS AND METHODS: Forty-four patients who underwent TTA due to extreme thrombocytosis between January 2000 and December 2021 in Erciyes University, Faculty of Medicine Therapeutic Apheresis Unit were analysed retrospectively. Extreme thrombocytosis was defined as a platelet count >
1000 × 10 RESULTS: The median percentage of platelet reduction was 62.2% (28.6%-90.1%). TTA was administered with Spectra Optia in 45.5% (n = 20) and Fresenius in 54.5% (n = 24) of the patients. No statistically significant difference was observed between age, gender, diagnoses, and devices used regarding TTA efficiency. The percentage of platelet reduction was higher in those who had a platelet precount above 1500 × 10 CONCLUSION: TTA provided prompt, effective, and safe reduction of platelet count in the treatment of extreme thrombocytosis.