In 1817, James Parkinson published his essay on the shaking palsy; a disease now well-known as Parkinson’s disease. In his essay, Parkinson described the characteristic motor features of PD. Nowadays however, it is recognized that PD is more than a pure motor disease, is also accompanied by cognitive impairment. Despite an increase of prognostic longitudinal studies that focus on the course of cognitive change in PD in the past decennia, much remains unclear about the pattern and profile of cognitive decline. In this thesis, we describe the course of cognitive change in a large sample of newly-diagnosed PD patients over the course of 5 years using a large neuropsychological test battery and with the inclusion of a control group. We show that memory impairment at time of diagnosis may be indicative of more rapid cognitive decline. Furthermore, cognitive impairment is an important predictor of functional decline. Although impairments are seen in multiple cognitive domains, we show that executive impairment lies at the core of the impairment. Additionally, we show that individual differences in motor symptom severity and cognitive dysfunction interact with response inhibition, and that extensive neuropsychological profiling may contribute to explaining, at least some, of the individual variation in reward-based learning in PD. Overall, our findings provide evidence that although dopamine depletion is characteristic of PD, the consequences of the disease are far more complicated and diverse. There is a need for more prospective studies that include a large neuropsychological test battery.