Secondary thrombocytosis, often referred to as a reactive thrombocytosis, is more common than primary thrombocytosis and has many potential etiologies including anemia, infection, inflammation, medications, and post-splenectomy. When considering the critically ill patient in the ICU setting potential medication-related etiologies of thrombocytosis should be included in the differential diagnosis. We present a 15-year-old adolescent with a traumatic brain injury who developed thrombocytosis that was temporally related to the administration of enoxaparin. There was a prompt return of the platelet count to normal following the discontinuation of enoxaparin therapy which led to the probable diagnosis of enoxaparin-induced thrombocytosis.