To measure maraviroc total cerebrospinal fluid (CSF) concentrations and compare them with total and unbound plasma concentrations. Total maraviroc was measured by reverse-phase high-performance liquid chromatography with tandem mass spectrometry, whereas ultrafiltration was used for unbound maraviroc. Maraviroc was detected in all nine CSF/plasma pairs with a median CSF total concentration of 2.4ng/ml. CSF concentrations exceeded the 50% inhibitory concentration of wild-type CC chemokine receptor 5-tropic HIV-1 in all specimens. CSF concentrations are lower than expected based on plasma concentrations and physicochemical characteristics. Unbound maraviroc plasma concentrations may be informative in estimating concentrations in CSF.