Gastrointestinal dysfunction is a frequent and occasionally dominating symptom of Parkinson's disease (PD). Features of gastrointestinal dysfunction include disordered control of saliva, dysphagia, gastroparesis, constipation in the sense of decreased bowel movement frequency, and defecatory dysfunction necessitating increased straining and resulting in incomplete evacuation. Excess saliva accumulates in the mouth because of decreased swallowing frequency. Dysphagia develops in approximately 50% of patients and may be a reflection of both central nervous system and enteric nervous system derangement. Gastroparesis may produce a variety of symptoms, including nausea, and also may be responsible for some of the motor fluctuations seen with levodopa therapy. Bowel dysfunction in PD may be the result of both delayed colon transit and impaired anorectal muscle coordination.