This study will evaluate the safety and efficacy of two dose levels of pimavanserin (ACP-103) compared to placebo in patients with Parkinson's disease psychosis.

• Experimental: pimavanserin tartrate (ACP-103) 20 mg, tablet, once daily by mouth, 6 weeks
• Placebo Comparator: Placebo tablet, once daily by mouth, 6 weeks
• Experimental: pimavanserin tartrate (ACP-103) 10 mg, tablet, once daily by mouth, 6 weeks

Inclusion Criteria:

• A clinical diagnosis of Parkinson's disease with a minimum duration of 1 year
• Presence of visual and/or auditory hallucinations, and/or delusions, occurring during the four weeks prior to study screening
• Psychotic symptoms must have developed after Parkinson's disease diagnosis was established
• Subject must be on stable dose of anti-Parkinson's medication for 1 month prior to Study Day 1 (Baseline) and during the trial
• Subject that has received stereotaxic surgery for subthalamic nucleus deep brain stimulation must be at least 6 months post surgery and the stimulator settings must have been stable for at least 1 month prior to Study Day 1 (Baseline) and must remain stable during the trial
• The subject is willing and able to provide consent
• Caregiver is willing and able to accompany the subject to all visits

Exclusion Criteria:

• Subject has a history of significant psychotic disorders prior to or concomitantly with the diagnosis of Parkinson's disease including, but not limited to, schizophrenia or bipolar disorder
• Subject has received previous ablative stereotaxic surgery (i.e., pallidotomy and thalamotomy) to treat Parkinson's disease
• Subject has current evidence of a serious and or unstable cardiovascular, respiratory, gastrointestinal, renal, mematologic or other medical disorder
• Subject has had a myocardial infarction in last six months
• Subject has any surgery planned during the screening, treatment or follow-up periods

Patients will be evaluated at screening to ensure that all criteria for study participation are met. These evaluations will include specific measures of psychosis severity, delirium, dementia, cardiovascular condition, and pregnancy status. Patients may be excluded from the study based on these assessments (and specifically if it is determined that their baseline health and psychiatric condition do not meet all protocol-specified entry criteria).