Hyperleukocytosis may be associated with an early morbidity and mortality due to leukostasis. Cytoreductive therapies-such as steroids, hydroxiurea, exchange transfusion, and leukapheresis-have been used for the prevention of leukostasis. Herein, the valproic acid used for the treatment of the hyperleukocytosis did not respond to known therapies in a child; lymphoblastic lymphoma developed bone marrow relapse under the treatment is discussed. © 2013 Informa Healthcare USA, Inc.