Objective: To report the clinical, electrophysiological, and immunological findings in one patient with MG and LEMS overlap syndrome (myasthenia gravis and Lambert-Eaton myasthenic syndrome). Methods: Evaluation of clinical, electrophysiological, and immunological findings in one patient with this disease. Results: A female patient with pernicious anemia had clinical findings of ptosis, diplopia, proximal leg weakness, areflexia and a positive edrophonium test as well as the classic patterns initially of MG and later of LEMS on successive repetitive nerve stimulation (RNS) tests. Immunologically she demonstrated positive acetylcholine receptor antibody (ACh-ab) and positive N-type voltage-gated calcium-channel antibody (VGCC-ab) titers. Conclusions: Among five reported cases combining the features of MG and LEMS and having positive AChR- and VGCC-ab titers, our patient provides the most convincing clinical, electrophysiological, and immunological evidence for the existence of MG and LEMS overlap syndrome. Significance: MG and LEMS overlap syndrome is a distinct entity. © 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.