Adverse events after vaccination against COVID-19 include rare events, such as Guillain-Barré syndrome. Study Aims. Documentation of clinical and temporary characteristics of the Guillain-Barré syndrome after using anti-COVID-19 ChAdOx1 nCoV-19 vaccine. Case Presentation. An adult, 29-year-old male, without relevant medical history, who developed neuromuscular symptoms nine days after administration of the first dose of anti-COVID-19 ChAdOx1 nCoV-19 vaccine.Symptoms appeared nine days after vaccination, with lower limbs paresthesia. Three days later, paresthesia of upper limbs occurred. The following day, distal weakness of limbs, with standing and gripping difficulties, occurred. The clinical evaluation demonstrated dysarthria, incomplete palpebral closure, bilateral facial, and tongue paresis. The electromyography was compatible with a motor demyelinating polyneuropathy, confirming the diagnosis of the Guillain-Barré syndrome. Management with five sessions of plasma exchange was prescribed, with favorable clinical results.Clinical and laboratory tests confirmed the Guillain-Barré syndrome and the time elapsed from the date of the vaccine administration to the appearance of initial symptoms, added to the absence of other causes, and allowed to establish that the disease was caused by the vaccination.