Myasthenia gravis (MG) is often complicated by respiratory failure, an exacerbation known as myasthenic crisis. However, most patients with MG develop respiratory symptoms during the late course of the disease. Respiratory failure as an exclusive initial and primary complaint in patients with MG is rare and seldom reported. We herein describe a woman in her late 50s who presented with respiratory failure and was diagnosed with obesity hypoventilation syndrome at a local hospital. Her condition gradually worsened during the next 4 months and became accompanied by dysphagia. After 1 year of medical investigation, she was diagnosed in our hospital. A high level of anti-muscle-specific receptor tyrosine kinase antibody was found in her serum, and stimulation and electromyography results suggested MG. The patient’s symptoms were improved by intravenous immunoglobulin and hormone therapy. This case reminds physicians to consider MG when encountering a patient who initially presents with respiratory failure.