In the present study, a sensitive and robust LC–MS/MS method has been developed and validated for the quantification of riluzole in human plasma and cerebrospinal fluid (CSF) in clinical samples from patients with spinal cord injury (SCI). Riluzole and its labeled internal standard (IS) were isolated from plasma and CSF by liquid–liquid extraction using ethyl acetate. Riluzole (m/z 235 → 166) and IS (m/z 238 → 169) were detected by electrospray ionization (ESI) using multiple reaction monitoring (MRM) in a positive mode. The assay was linear in the concentration range of 0.5 (LLOQ, signal/noise ratio > 10)–800 ng/ml in plasma, and 1.0 (LLOQ)–800 ng/ml in CSF samples. The intra- and inter-day accuracy in plasma were 94.2–110.0% and 97.8–102.0%, respectively, and those in CSF were 87.6–105.1% and 91.9–98.8%, respectively. The intra- and inter-day precision were 2.2–7.2% and 4.0–9.1%, respectively, in plasma, and 1.4–14.1% and 2.6–11.5%, respectively in CSF. Matrix effect was negligible from both matrices with signal percentages of 97.6–100.6% in plasma and 99.4–106.4% in CSF. The recoveries were >75% in plasma, >84% in CSF with low protein (53.9 mg/dl), and >68% in CSF with high protein (348.2 mg/dl). This method was successfully applied to quantify riluzole concentrations in plasma and CSF from patients with SCI.