There are acute and chronic Lyme neuropathies. The seasonal acute syndromes of cranial neuritis or radiculoneuritis are generally quite distinctive, but may cause diagnostic difficulty when one syndrome occurs without the other, when erythema migrans is absent or missed, and when meningeal signs are minimal or absent. The chronic Lyme radiculoneuropathies are less severe, and less distinctive. Their recognition depends on eliciting a history of earlier classical manifestations of Lyme disease and by laboratory testing. In both acute and chronic Lyme radiculoneuropathy, electrophysiologic testing often proves the presence of a sensorimotor, axon loss polyradiculoneuropathy. Both acute and chronic Lyme radiculoneuropathy have similar pathologic features and can be classified as a nonvasculitic mononeuritis multiplex. The pathogenesis is uncertain; both direct infection as well as parainfectious mechanisms may play a role. The treatment with which we have the most experience is intravenous ceftriaxone 2 g/day for 2 to 4 weeks. Improvement occurs rapidly over days to weeks in early Lyme neuroborreliosis, but slowly over many months in chronic neuroborreliosis.