Non-motor symptoms (NMS) of Parkinson's disease (PD) are a key determinant of health, quality of life (QoL) and societal cost of PD. They are often less appreciated than motor symptoms but are important sources of disability for manyPDpatients. Literature search was performed using the reference databases Medline, Science Citation Index and EMBASE. The keywords used were 'non-motor symptoms', Parkinson's disease, olfaction and constipation. Papers discovered by this search were reviewed, as were references cited therein. Contrary to common perception, many NMS of PD occur early in PD and some may even predate the diagnosis of PD that is based on motor signs. These include olfactory deficit, sleep problems such as rapid eye movement behaviour disorder, constipation and the more recently described male erectile dysfunction. There is compelling evidence that nonmotor symptoms of PD play a dominant role in the QoL and disability of PD patients and the QoLof their 'informal' carers. Effective clinical management of PD therefore demands that these symptoms be identified and to the extent possible treated.