A 2.5-year-old boy presented to his pediatrician with progressive pallor, asthenia, fever, splenomegaly, and hematomas. Leukemia was suspected, and a bone marrow aspirate confirmed acute lymphoblastic leukemia. Before chemotherapy induction, the child developed a vesicular rash and was diagnosed clinically with chickenpox. Acyclovir treatment was initiated immediately, whereas induction chemotherapy was postponed by 10 days. At the time of chickenpox resolution, a spontaneous partial recovery of his blood counts and a 50% decrease of blastic bone marrow infiltration were noted. After a brief nonsystematic review, we discuss the potential beneficial effect of acyclovir and chickenpox infection in children with leukemia.