Reactive thrombocytosis can be seen in patients with various kinds of infections, including upper urinary tract infection. Thrombocytosis in patients with upper urinary tract infection is a response of the bone marrow to the infection and is therefore classified as secondary thrombocytosis. We report a case of thrombocytosis accompanying renal abscess. In this case report, we present that thrombocytosis in a patient with upper urinary tract infection is not a random condition and is associated with renal abscess which is a complication of disease.