Thrombocytosis is a frequently seen condition during childhood. While it usually develops secondarily due to reasons such as infection or anemia, it may rarely develop due to clonal causes. Thrombocytosis becomes a life-threatening condition by causing severe complications such as hemorrhage and thrombosis development. Treatment is not recommended in patients who are asymptomatic and with a platelet count below 1,500,000/mm3, however, treatment is required in cases who are symptomatic and with a platelet count above 1,500,000/mm3 in conditions such as primary thrombocytosis. This article present the outcomes of a patient who was treated using low-dose hydroxyurea when he developed severe thrombocytosis after splenectomy.