There is growing recognition that gastrointestinal dysfunction is common in Parkinson's disease (PD). Virtually all parts of the gastrointestinal tract can be affected, in some cases early in the disease course. Weight loss is common but poorly understood in people with PD. Dysphagia can result from dysfunction at the mouth, pharynx, and oesophagus and may predispose individuals to aspiration (accidental inhalation of food or liquid). Gastroparesis can produce various symptoms in patients with PD and may cause erratic absorption of drugs given to treat the disorder. Bowel dysfunction can consist of both slowed colonic transit with consequent reduced bowel-movement frequency, and difficulty with the act of defecation itself with excessive straining and incomplete emptying. Recognition of these gastrointestinal complications can lead to earlier and potentially more effective therapeutic intervention.