Background: The presence of both myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) in one patient is very rare. Here, we report the case of a patient with these coexisting conditions. Case Presentstion: An 82-year-old man with a history of adenocarcinoma of the bladder was referred to the neurology ward with diplopia, dysphagia, ptosis in the left eye, weakness in both lower extremities, and autonomic dysfunction. Coexistence of MG and LEMS was diagnosed according to clinical and para-clinical evaluations. Conclusion: Coexistence of MG and LEMS is very rare, but this presentation in a patient with a history of adenocarcinoma of the bladder has not been previously reported. We emphasize the importance of carefully evaluating patients with LEMS for any underlying malignancy