The neurological spectrum of Borrelia burgdorferi infections is still enlarging. We review epidemiological, pathological and serological data of Lyme disease. The course of the disease is divided in three stages: stage 1 during the first month is characterised by erythema chronicum migrans and associated manifestations; stage 2 includes not only the classical European meningoradiculitis but also less specific neurological symptoms: isolated lymphocytic meningitis with an acute or even relapsing course, apparently idiopathic facial palsy, neuritis of other cranial nerves, polyneuritis cranialis, Argyll-Robertson sign, peripheral nerve involvement, acute transverse myelitis, severe encephalitis, myositis. During stage 3, three to five months or longer after the onset of the disease, chronic arthritis, acrodermatitis chronica atrophicans and various neurological symptoms can be observed: chronic neuropathy with mainly sensory or motor signs, recurrent strokes due to cerebral angiopathy and progressive encephalomyelitis; this third stage the central nervous system involvement is characterised by slowly progressive or fluctuating course during months or years, ataxic or spastic gait disorder, bladder disturbances, cranial nerve dysfunction including optic atrophy and hypoacusia, dysarthria, focal and diffuse encephalopathy. This chronic central nervous system disease can mimic multiple sclerosis, anorexia nervosa, psychic disorders or subacute presenile dementia. It is often associated with pleiocytosis, abnormal EEG and evoked potentials, sometimes multifocal and mainly periventricular white matter lesions visualised by CT or MRI, and as a rule high antibody titers against Borrelia burgdorferi. High doses of penicillin can halt the disease, sometimes induce spectacular regression of symptoms or sometimes be inefficient; ceftriaxone could be a more powerful therapy. Similarities between syphilis and Borreliosis are multiple: both of these spirochetes contain plasmids, can be transmitted through the placenta and progress for many years through successive stages, with multiorgan symptoms, including parenchymatous and vascular lesions of the central nervous system. Borrelia burgdorferi is the new great imitator.