A 5-year-old boy with acute lymphoblastic leukemia (ALL) and intolerance to oral trimethoprim-sulfamethoxazole (TMP/SMX) had Listeria monocytogenes bacteremia and meningitis develop during maintenance chemotherapy. Despite prompt administration of IV amoxicillin/gentamicin and microbiologic clearance of the bloodstream, the patient had no response to therapy after a course of 7 days. Intravenous TMP/SMX (10 mg/kg per day of TMP) was added to the antibiotic regimen after desensitization. Fever and meningeal signs rapidly resolved, and the patient was ultimately cured. Amoxicillin and gentamicin, although highly active and synergistic in vitro against L. monocytogenes, have limited intracellular penetration and activity. In contrast, TMP/SMX has bactericidal extracellular and intracellular activity against Listeria and excellent central nervous system penetration, and thus may be effective for the treatment of refractory listeriosis.