Neuropsychiatric symptoms (NPS) of Parkinson's disease (PD) are of growing diagnostic and therapeutic importance. Data on their prevalence and characteristics have been primarily derived from highly selective clinical populations. We have conducted a national study in the outpatient care sector to provide a fuller characterization of the frequency of dementia, depression, and other NPS in PD outpatients. We also examined associations with biosocial and neurological variables. A nationwide representative sample of 1,449 PD outpatients was examined with a standardized clinical interview. PD severity was rated with the Hoehn and Yahr (HY) scale and the Unified Parkinson's Disease Rating Scale. Depression was measured with the Montgomery-Asberg Depression Rating Scale. Cognitive impairment and dementia were assessed with the Mini-Mental State Exam and according to diagnostic criteria. Logistic regression analyses were used to investigate associations. At least one NPS occurred in 71% of all patients with PD. The estimated prevalences (ranges) by age group and HY-stage were: depression, 25% (13.2-47.9%), dementia, 29% (12.2-59.4%), and psychotic syndromes, 12.7% (3.1-40.9%). Other frequent complications were sleep disturbances (49%) and anxiety (20%). Depression was associated with gender but not with age. Dementia was associated with age. The rates and comorbidity of depression and dementia were driven by PD severity. NPS were highly prevalent in our comprehensive patient sample, largely representative of management problems occurring in an outpatient setting. PD outpatients are at an increased risk for all neuropsychiatric conditions, increasing with PD severity but not with age or age of onset (except dementia), revealing challenging symptom patterns.