A 20-year-old woman with a history of intravenous drug use and previous methicillin-resistant Staphylococcus aureus (MRSA) endocarditis was admitted with a 1-week history of fever, headache, and confusion. Her cerebrospinal fluid (CSF) revealed 83 × 106/L nucleated cells with 61% neutrophils and 29% lymphocytes. CSF cultures grew MRSA. Antibiotics were started and an extraventricular drain was placed. One week later another lumbar puncture showed 440 × 106/L nucleated cells with 61% plasma cells, 28% lymphocytes, and 5% neutrophils. Numerous plasma cells were identified on a cytospin preparation (see figure). Peripheral blood neutrophilia (19.3 × 109/L) and normocytic anemia (hemoglobin 105 g/L) resolved at time of discharge. No serum protein electrophoresis was performed and there was no evidence of underlying malignancies or HIV. The patient recovered with only mild word-finding difficulties. The presence of CSF plasmacytosis is unusual but nonspecific. It has been associated with ce