The concurrent development of Guillain-Barré syndrome (GBS) and myasthenia gravis (MG) is rare. It has been associated with molecular mimicry between infectious agents and self-antigens. Such antibodies may show cross-reactions against both myelin proteins of peripheral nerves and acetylcholine receptors of neuromuscular junctions. Thymoma-associated multi-organ autoimmunity may also play a role in initiating autoimmune process. We present such a case with the concurrent development of GBS and MG.