During the 2 year award period, we will prospectively enroll 200 patients with idiopathic Parkinson Disease (PD), who meet eligibility criteria below. All patients will undergo a baseline polysomnography (PSG) to diagnose Sleep Disordered Breathing (SDB) and will be asked to complete validated questionnaires to measure Sleep Quality, SDB risk, insomnia severity, daytime sleepiness, presence of restless leg syndrome (RLS), anxiety/depression, and quality of life. Medical records will be reviewed to determine co-morbidities and medication use. Each PD participant will undergo a full neurological examination, including the Unified Parkinson's Disease Rating Scale (UPDRS), the Hoehn & Yahr stage and a battery of neuro-cognitive measures at baseline. Patients with SDB will be offered PAP titration and treatment for 4 months. All patients (SDB [PAP compliant, non-compliant], and no SDB [controls]) will complete repeat neuro-cognitive evaluation, questionnaires, neurological evaluation and UPDRS assessment at 4 month and at 1 year follow-up. PD participants will be assessed in the "on" state in the morning. In the event that a participant goes "off" during testing, a break will be taken and participants will be given the option of taking their medication to return to the "on" state and resume testing or they can return later in the week to complete the evaluation. Although participants will understand the general purpose of the study, they will be blinded to the major study hypothesis. Neuropsychological examiners and the neurologist conducting the neurological exam will be blinded to the SDB status of the patient. Four month follow-up will be staggered according to enrolment date and will be completed by Year 2.