Unilateral laterothoracic exanthem (ULE) is a rare childhood condition of unknown etiology characterized by a morbilliform rash that usually begins in the axilla and spreads centrifugally. The condition is usually self-limited, does not require specific treatment, and disappears within 4 to 6 weeks. Pruritus may be relieved by oral antihistamines and topical emollients and/or bath oils. We describe ULE in a 6-year-old girl with acute lymphoblastic leukemia, the first report of ULE in a patient with malignancy.