Background: A DNA target imbalance in favor of the plasmid-borne outer surface protein A (OspA) versus chromosomal genes has been thought to explain the relatively high diagnostic sensitivity of an OspA-based polymerase chain reaction (PCR) on joint fluid from patients with Lyme arthritis. The aim of this study was to evaluate the diagnostic sensitivity of the OspA-based PCR on cerebrospinal fluid (CSF) samples from patients with Lyme neuroborreliosis and to perform DNA sequence analysis on the amplicon to determine the genospecies of Borrelia present in the CSF. Methods and Results: CSF from 150 consecutively diagnosed European patients with untreated active neuroborreliosis was investigated. Borrelia burgdorferi DNA was detected in 31 of 150 patients with Lyme neuroborreliosis (20.6%). Genotyping of the amplicons was possible in 13 of the CSF samples and revealed that 11 of the 13 patients had been infected with Borrelia garinii, 1 with Borrelia afzelii, and 1 specimen showed evidence of a mixture of B. garinii and B. afzelii sequences. Conclusions: The diagnostic sensitivity of the OspA-based PCR for detection of B. burgdorferi DNA in CSF was comparable to that found previously using PCR assays based on genomic targets. The predominance of B. garinii DNA (92%) found in CSF substantially supports the current hypothesis that B. garinii is the principal agent of Lyme neuroborreliosis in Europe. Mixed infections, comprising different genospecies of B. burgdorferi sensu lato, seem to be the exception.