The Eaton-Lambert syndrome is a clinical and electrophysiological entity, which affects less than 3% of patients with a small cell cancer. In the majority of cases the syndrome is present before the discovery of cancer. The diagnosis is primarily suggested by proximal muscle fatiquibility in the lower limbs. The confirmation of the diagnosis is carried out by an electromyography. The occurrence of non-para neoplastic cases are frequently associated with disorders of immunity (Auto-immune Disease, and various auto-antibodies) in the groups HLA B8 and DR3. The efficacy of immunosuppressants has led to a search for an auto-immune mechanism as the basis for this myasthenic type syndrome. The demonstration in recent years of anti-calcium channel antibodies at the origin of the pre-synaptic junctional block has confirmed this hypothesis. The demonstration of the auto-immune character of this para-neoplastic syndrome has led to better understanding of the host tumour relationship from an immunopathological stand point.