Although rare, neutropenia associated with long-term vancomycin therapy may occur. A 67-year-old woman with cellulitis and sepsis caused by Staphylococcus aureus was treated initially with cefazolin. Despite in-vitro susceptibility of the organism to this drug, the patient remained febrile, and therapy was changed to vancomycin. On day 17 of therapy with this medication neutropenia was noted; it progressed over the next 3 days, and therapy with the drug was stopped. A rise in the neutrophil count occurred within 5 days of discontinuation. Periodic monitoring of the leukocyte count during longterm vancomycin therapy is recommended.