Patients with myasthenia gravis (MG) rarely complain lower urinary tract (LUT) dysfunction, even though they may have, since blephaloptosis, extraocular muscle weakness and limb weakness are the major problems for the patients. MG is a relatively common neuromuscular junction disorder. We recently found that 30% of patients with generalized MG had LUT dysfunction, which was more common than that in control population, and it affected the quality of life of the patients. In female patients stress urinary incontinence due to sphincter and pelvic floor weakness was the most common, whereas male patients might have overactive bladder due to bladder irritation by anti-cholinesterase treatment, and polyuria due to corticosteroids. In conclusion, patients with MG may have LUT dysfunction mainly of sphincter etiology. Amelioration of LUT dysfunction, particularly of stress urinary incontinence that affects the quality of life, therefore should be a primary target in the treatment of patients with MG.