Hyperleukocytosis (white blood cell count, >100×109/l), an uncommon presentation of leukemia, is associated with an increased risk of early mortality. It may present with a variety of symptoms secondary to leukostasis, a syndrome caused by the sludging of circulating leukemic blasts in the microvasculature. Adequate measures for managing this medical emergency include hydration, cytoreduction, prevention of tumor lysis and, rarely, leukapheresis in cases complicated by leukostasis and hyperviscosity syndrome. The present study reports a case series of five patients with hyperleukocytic leukemia. In addition, a review of the literature with regard to the incidence, pathophysiology, clinical manifestations and management of this laboratory abnormality is included. This study demonstrated that the central nervous system and lungs are the most common sites for leukostasis, and that emergency cases require aggressive treatment.