Glial fibrillary acidic protein astrocytopathy (GFAP-A) is a recently recognized autoimmune disorder affecting the central nervous system, with predominant involvement of the brain, meninges, spinal cord, and optic nerves. Although frequently associated with neoplasms, its co-occurrence with laryngeal carcinoma remains undocumented. We describe a 70-year-old male patient presenting with progressive lower limb weakness and bowel/bladder dysfunction evolving over two weeks. Six months earlier, he had been diagnosed with laryngeal squamous cell carcinoma, and underwent surgical resection followed by adjuvant radiotherapy and chemotherapy. Cerebrospinal fluid (CSF) analysis demonstrated pleocytosis (67 × 106/l) with 92% mononuclear predominance. Critically, GFAP antibody testing of the cerebrospinal fluid confirmed positivity. This patient has been diagnosed with autoimmune GFAP myelitis with laryngeal cancer. Immunotherapy comprised intravenous methylprednisolone (initial 480 mg/day), tapered to 60 mg, followed by biweekly 5 mg reductions. Concurrently, neurotrophic therapy was administered. After immunomodulation, the patient demonstrated marked resolution of chest tightness and bowel/bladder dysfunction. Urinary catheter removal coincided with improved lower limb strength (bilateral IV+), allowing independent ambulation at reduced velocity. Subsequently, the patient was discharged. In conclusion, following laryngeal cancer surgery, new-onset lower limb weakness with bowel/bladder dysfunction warrants consideration of autoimmune GFAP myelitis alongside spinal metastases in differential diagnosis. Prompt neuroaxis MRI (cranial/cervical/lumbar) and cerebrospinal fluid GFAP antibody testing are essential to mitigate diagnostic delays.