There is much excitement around the use of advanced therapy medicinal products (ATMPs), including cell and gene treatments, in Parkinson's disease (PD). However, taking an ATMP to clinical trials in patients with PD is complex. As such it is important from an investigator's perspective that they ask themselves two key questions before embarking on such work: firstly, why are you doing it, and, secondly, do you understand what is needed to conduct a clinical trial with that product. In this article, we briefly discuss these two questions.