Peripheral nerve dysfunction was demonstrated in 36% of patients with late Lyme disease. Of 36 patients evaluated, 14 had prominent limb paresthesias. Thirteen of these had neurophysiologic evidence of peripheral neuropathy; neurologic examinations were normal in most. Repeat testing following treatment documented rapid improvement in 11 of 12. We conclude that this neuropathy, which is quite different from the infrequent peripheral nerve syndromes previously described in this illness, is commonly present in late Lyme disease. This neuropathy presents with intermittent paresthesias without significant deficits on clinical examination and is reversible with appropriate antibiotic treatment. Neurophysiologic testing provides a useful diagnostic tool and an important measure of response to treatment.