Neuromyelitis optica (NMO or Devic's syndrome) is a rare relapsing demyelinating disease of the central nervous system (CNS) that mainly affects the spinal cord and optic nerves and shares many clinical and radiological features with multiple sclerosis. The association of NMO with other autoimmune diseases was reported, but very few reports described association with autoimmune thyroid disease. Early differentiation between NMO and multiple sclerosis is very important as the natural course and treatment regimens differ significantly. We report a case of a 50-year-old woman who was admitted initially with vomiting, hiccups and paraesthesias but was not diagnosed with NMO and presented with a severe progression of the disease. The patient was also diagnosed to have autoimmune thyroiditis with lymphocytic infiltration of the thyroid which progressed from hyperthyroidism to hypothyroidism. NMO diagnosis was established with seropositivity for NMO-IgG and MRI showing longitudinally extensive spinal cord lesions (3 or more spinal segments). In spite of treatment, the response was poor due to lack of early diagnosis and aggressive immunosuppressant therapy.