Our report describes a previously healthy 10-year-old female who was seen for urticarial plaques and mild loss of appetite. An initial laboratory workup revealed an elevated leukocyte count of 30,000/microL and a peripheral eosinophil count of 22,500/microL. A skin biopsy showed a marked hypersensitivity tissue response with abundant eosinophils. Further investigation of her peripheral eosinophilia uncovered Giardia lamblia in a stool sample. Despite treatment with the anti-parasitic agent furazolidone, the patient's urticarial plaques, leukocyte count, and peripheral eosinophil count remained unchanged. A bone marrow biopsy confirmed a diagnosis of acute lymphoblastic leukemia (ALL). ALL with hypereosinophilia (ALL/Eo) represents a rare and distinct subset of ALL, with more than 30 cases documented in the literature. Our discussion summarizes the clinical aspects of this disease and reviews the reported dermatological manifestations of ALL/Eo.