BACKGROUND & AIMS: Diagnostic procedures in Whipple's disease usually focus on the intestine, but symptomatic central nervous system involvement is a major threat for patients. The aim of this study was to determine the diagnostic value of cerebrospinal fluid (CSF) analysis. METHODS: A total of 39 CSF samples and 2 brain biopsy specimens that were obtained from 24 patients with Whipple's disease at various intervals after diagnosis were examined. Five patients presented with neurological symptoms, 3 of them as relapses after therapy. Thirty-two CSF samples were examined by polymerase chain reaction for Tropheryma whippelli and 20 CSF samples by cytology. Brain biopsy specimens were examined histologically. RESULTS: Positive results were obtained in 4 of 5 patients (80%) with neurological symptoms, in 7 of 10 patients (70%) without neurological symptoms examined before therapy, and in 3 of 11 patients (27%) without neurological symptoms studied during or after therapy. Conversion from positive to negative was observed in 4 patients after antibiotic treatment. CONCLUSIONS: Testing of CSF in Whipple's disease yields a high rate of positive results, even in patients without neurological symptoms. Examination of CSF is therefore potentially useful for initial staging and for monitoring of the efficiency of therapy.