Objective: To compare the efficacy of conventional cytomorphologic analysis and flow cytometry (FC) in the diagnosis of T-cell lymphoma in the cerebrospinal fluid (CSF). Study Design: We performed a retrospective review of CSF samples from 2002 to 2012 that showed involvement of a T-cell lymphoma, either by cytomorphologic analysis and/or FC. Patients' demographics, clinical history and follow-up were assessed. Results: Thirty-nine CSF samples were identified from 9 patients. A definitive diagnosis of T-cell lymphoma involvement was made by cytomorphologic analysis and FC in 6 (15.4%) and 39 (100.0%) specimens, respectively. In specimens with definitive cytopathologic diagnoses, the cytomorphologic features included increased cellularity, a monotonous lymphoid population and large, atypical lymphoid cells. Considering cytomorphologic features only, 9 specimens demonstrated atypical lymphocytes not fulfilling the criteria for malignancy, and 24 specimens were negative for malignancy. Conclusions: CSF with T-cell lymphoma involvement may yield paucicellular or acellular specimens depending on the volume of the CSF, the time interval between specimen collection and specimen processing and the application of preservative to CSF. The rate of detection of T-cell lymphoma in the CSF by FC is unequivocally higher than by cytomorphologic analysis. Careful attention to clinical history is crucial, as FC testing may be tailored to evaluate for T-cell lymphoproliferative disorders in limited samples.