The objective of this study was to examine the validity of the mentation, behavior, and mood items included in Part I of the Unified Parkinson's Disease Rating Scale (UPDRS) and to assess its usefulness to screen for dementia, psychosis, depression, and apathy. A consecutive series of 168 patients with PD were assessed by neurologists with the UPDRS, and by psychiatrists using a comprehensive neuropsychiatric evaluation blind to each other's ratings. ROC analysis demonstrated that a score of 2 or greater on the intellectual impairment item of the UPDRS had 60% sensitivity and 92% specificity to detect dementia, as diagnosed with DSM-IV criteria. When a score of 23 or lower on the MMSE was included as an additional classification variable, the sensitivity increased to 85%. A score of 2 or greater on the thought disorder item had 43% sensitivity and 92% specificity to detect psychotic symptoms (delusions or hallucinations). A score of 2 or greater on the depression item had 77% sensitivity and 82% specificity to detect major depression as diagnosed with DSM-IV criteria. Finally, a score of 2 or greater on the motivation/initiative item had 73% sensitivity and 65% specificity to detect apathy, as diagnosed with a standardized criteria. When the sample was divided into mild (i.e. Hohen-Yahr stages I and II) versus moderate-severe PD (i.e. Hohen-Yahr stages III-V), findings remained unchanged, except that the UPDRS show unacceptably low accuracy to detect psychosis in mild PD. The mentation, behavior, and mood section of the UPDRS is an adequate screen for depression and apathy, and has adequate sensitivity to detect dementia when combined with the Mini-Mental State Exam, but has low sensitivity to detect psychosis. (c) 2007 Movement Disorder Society.