Parkinson’s disease is a slowly progressive and irreversible disorder of the nervous system. Drooling is listed as a secondary symptom of Parkinson’s disease. Its cause is insufficiently clear. In the literature 2 possible causes are described: hypersalivation and swallowing abnormalities. These parameters have not been measured in a single study before. This article presents a review of the literature on the subject and describes the design for a future clinical study. The aim of this clinical study is to gain an insight into the cause and the prevalence of drooling in Parkinson’s patients. A group of 50 Parkinson’s patients will be compared to a group of 50 controls. The objectives of this comparative study comprise the assessment of salivary flow volumes, swallowing capacity, subjective experiences with drooling and an objective observation of drooling, the drooling quotient. Finally, the possibilities for treatment will be described.