We report four cases of Lambert-Eaton myasthenic syndrome (LEMS) or myasthenia gravis (MG) associated with pulmonary neuroendocrine carcinoma having prolonged survival. The tumors were atypical carcinoid or large cell neuroendocrine carcinoma. LEMS is associated with several neuroendocrine carcinomas. Because some neuroendocrine carcinomas have a better prognosis, aggressive tissue diagnosis of lung cancer in LEMS is warranted. Whether the association between MG and atypical carcinoid is a significant co-occurrence is uncertain.