The purpose of this study was to evaluate the influence of plasmapheresis on sleep in patients with generalized myasthenia gravis and no respiratory symptoms. Seven myasthenia gravis patients, four women and three men, aged 24-52 years, underwent plasmapheresis treatment because of recent worsening of clinical weakness and poor response to previous treatments. We prospectively recorded the myasthenia gravis score, measured acetylcholine-receptor antibody concentration, performed polysomnography, and checked the Epworth Sleepiness Scale at baseline and 1 day after completion of the last session of plasmapheresis. Myasthenic weakness was ameliorated following plasmapheresis in all patients with a median decrease in myasthenia gravis score of 2 points (P = 0.0002) and a median clearance of 43.3% of acetylcholine-receptor antibody. However, there was no significant change in polysomnographic parameters, except for a trend toward shorter duration of the longest apnea period (P = 0.0763) following the treatment. Plasmapheresis did not affect polysomnographic parameters despite improved clinical weakness along with decreased myasthenia gravis score and acetylcholine-receptor antibody concentration.