BACKGROUND Mild disorders associated with persistent neonatal myasthenia gravis may not be recognized for several months. Esophageal dysfunction in this type of myasthenia has never been studied. CASE REPORT A gastroesophageal reflux was diagnosed during the first weeks of life in a girl; she was not treated. At 8 month-old, she was admitted for febrile convulsions; the pyrexia was due to urinary tract infection by Escherichia coli. 4 days later, the infant displayed weakness of the eyelids and extraocular muscles. The proximal muscles of the arms were also weak. Neostigmine, 0.3 mg subcutaneously, completely removed the symptoms in a few minutes. Neuromuscular transmission tests showed a progressive decrease in eyelid muscle response on repetitive stimulation of the nerve, with a pattern of post-synaptic defects that was corrected by edrophonium chloride injection. Neither the girl nor her mother had acetylcholine receptor antibodies. Overnight monitoring of the distal esophagus pH showed numerous episodes of acid reflux, essentially after the meal. Manometry disclosed abnormalities of both the striated and smooth muscles of the esophagus that were corrected with neostigmine. The girl was given neostigmine and was in good condition one year later. CONCLUSION Myasthenia could worsen and/or trigger a gastroesophageal reflux by decreasing esophageal clearance and lower esophageal sphincter pressure.