Lyme disease is a multisystem infectious disease caused by tick-borne spirochetes of the Borrelia burgdorferi group. The disease occurs primarily in specific areas of North America, Europe and Asia, reflecting the distribution of the hard-shelled Ixodes ticks that are required for disease transmission. Diagnosis of this infection can be somewhat problematic, although in clinically appropriate settings, serologic testing can be highly useful, particularly if Western blots are used to confirm borderline or positive results. The organism has several specific organotropisms-involvement of the heart, joints and nervous system being particularly common. The nervous system can be involved in one or more ways. Early in infection, patients tend to get a lymphocytic meningitis, cranial neuritis (particularly the facial nerves) or a painful radiculitis. Rarely, an encephalomyelitis can occur. In patients with more protracted and indolent involvement, a more disseminated mononeuropathy multiplex may occur, or a mild, non-focal alteration of cognitive function and memory, i.e. an encephalopathy. In patients with central nervous system involvement, the most sensitive diagnostic test is the demonstration of intrathecal production of anti-Borrelia burgdorferi antibody. Culture, polymerase chain reaction and other techniques appear to be less specific. In most instances, the disease is quite responsive to antimicrobial therapy. Oral treatment with doxycycline has been shown to be effective in meningitis. In more serious cases two to four week courses of parenteral ceffriaxone or cefotaxime are effective in the vast majority of patients.