The nonmotor symptoms (NMS) of Parkinson's disease (PD) are less well recognised and can be more troublesome to patients and carers than classical motor features. NMS are frequently missed during routine consultations and such under-recognition may have implications on quality of care given that many NMS are treatable. To determine the proportion of patients not declaring NMS to healthcare professional (HCP) as assessed by self completion of the NMS questionnaire (NMSQuest), a validated, self-completing questionnaire with 30 items. Multicentre international study. The data was collected from PD patients across all age groups and stages attending outpatient clinics in specialist and care of the elderly settings. 242 patients recruited and undeclared NMS ranged from 31.8% (diplopia) to 65.2% (delusions). The most frequently nondeclared symptoms were delusions, daytime sleepiness, intense and vivid dreams, and dizziness. In many, appropriate treatments for undeclared NMS were started only after these were recognised following completion of NMSQuest. NMS of PD are frequently undeclared at routine hospital consultation and may be related to the fact that patients often do not link these symptoms with PD or may be too embarrassed to discuss these. Use of NMSQuest allows patients to flag symptoms which may be otherwise undeclared and remain untreated when potential treatments exist.