Guillain-Barre syndrome (GBS) is a rare neurological disorder in which the immune system mistakenly attacks part of the peripheral nervous system, which is the network of nerves outside the brain and spinal cord. The exact cause of GBS is unknown, but most cases follow an infection with a virus or bacteria, such as Campylobacter jejuni, which causes gastroenteritis. In GBS, the immune system attacks the nerves protective covering, preventing the nerves from transmitting signals to the brain, causing weakness, numbness, or paralysis. The symptoms of GBS can increase in intensity over a period of hours, days, or weeks until certain muscles cannot be used at all, and when severe, the person is almost totally paralyzed. The most common initial symptoms of GBS are weakness and tingling in the hands and feet, which can quickly spread, eventually paralyzing the whole body. GBS can be a devastating disorder because of its sudden and rapid, unexpected onset of weakness and usually actual paralysis, but most people with GBS have a full recovery with careful intensive care and successful treatment of infection, autonomic dysfunction, and other medical complications.