Idiopathic parkinsonism (IP) is associated with substantia nigra and platelet mitochondrial hypofunction. Since dopaminergic neurone loss is found in the enteric nervous system, it was proposed that the mitochondrial damage may extend to enterocytes and be responsible for abnormal bowel function. Oesophago-gastro-duodenoscopy was carried out to confirm eradication of (culture-positive) Helicobacter pylori (Hp) infection in IP. Transmission electron microscopy of duodenal enterocytes revealed double-membrane encapsulated filamentous arrays, but no intra- or extra-cellular Helicobacter. These bodies were present in one/both biopsies from half of the probands with successful Helicobacter eradication, defined by histopathology, culture and molecular-biology. The serum anti-Hp antibody profile predicted abnormal bowel function.