Parkinson's disease (PD) is a degenerative sub-cortical neurological disorder primarily involving morphologic and neurochemical changes in the human brain, particularly the basal ganglia. Basal ganglia is a term used to identify areas of the basal forebrain and midbrain known to be involved in the control of movement and some higher cortical functions. Cardinal motor symptoms in PD include muscle rigidity, tremor, bradykinesia, a loss of postural reflexes and, in extreme cases, akinesia. These symptoms can be experienced either unilaterally or bilaterally. Non-motor symptoms in PD include cognitive decline, depression, sleep disturbances, hallucinations, and apathy. Changes in cognitive functioning in PD can range from mild cognitive impairment to Parkinson's disease dementia (PDD). While studies investigating a potential relationship between motor symptom phenotype and cognitive decline in PD exist, results have been equivocal to date. Additional research has been recommended and this was the aim of the current studies. Participants (n = 88) were recruited from the Royal Hobart Hospital and administered a comprehensive assessment battery that included demographic and mood measures, a range of cognitive measures covering immediate and delayed memory, executive functioning, visuospatial functioning, and language, as well as several tests of motor functioning. Study One examined the link between current motor functioning and cognitive performance. Despite no significant between groups differences on demographic variables such as age, years of education, pre-morbid cognitive functioning, mood, and disease duration, participants in the lower motor functioning group consistently performed more poorly on all cognitive tasks included in the assessment battery. Study Two examined the impact of side of motor symptom onset, comparing the current cognitive functioning of participants who experience left sided, right sided, or bilateral motor symptoms at time of initial diagnosis. While no significant differences were found between those with left sided and right sided motor symptom onset, those with bilateral motor symptom onset were significantly (p < .001) more likely to achieve the poorest cognitive results. Study Three examined the potentially confounding impact of motor functioning and side of onset when assessing anxiety and depression in a PD population using the two-factor Hospital Anxiety and Depression Scale (HADS) as well as a three-factor model of the HADS that separated anxiety, depression, and psychomotor symptoms. Results cautioned against reliance on the traditional HADS for detecting mood symptoms in people with PD. Overall results indicate that motor symptom presentation can provide valuable information regarding cognitive functioning and mood in PD populations.