Achalasia and Parkinson's disease sometimes have similar clinical and neuropathologic features, including loss of esophageal peristalsis and neuronal loss within brainstem nuclei. We compared the neuropathologic features in autopsies of 8 achalasia patients, 22 Parkinson's disease patients (3 patients with dysphagia), and 50 age- and sex-matched controls. Degenerating ganglion cells in the esophageal myenteric plexus in 2 achalasia patients contained Lewy bodies, intracytoplasmic inclusions characteristically found in the brainstem in Parkinson's disease. Esophageal or colonic Lewy bodies were also found in 2 Parkinson's disease patients with dysphagia. No gastrointestinal tract Lewy bodies were identified in Parkinson's disease patients without dysphagia or in controls. One achalasia patient with esophageal Lewy bodies also had the inclusions and neuronal depigmentation in the vagal dorsal motor nucleus and substantia nigra, as seen in Parkinson's disease. Our findings indicate that a subset of achalasia and Parkinson's disease patients with dysphagia may have similar mechanisms of neuronal degeneration responsible for esophageal dysfunction.