There have been several recent scientific advances in gene-based and cell-based therapies that might translate into novel therapeutic approaches for neurodegenerative disorders. Such therapies might need to be directly delivered into the CNS, and complex scientific and ethical assessment will be needed to determine whether a sham neurosurgical arm should be included in clinical trials assessing these agents. We have developed a framework of points for investigators to consider when designing trials that involve direct delivery of a therapeutic agent to the CNS. The inclusion of a sham neurosurgical arm will be guided in part by the objectives of the clinical study (preliminary safety, optimisation, and feasibility vs preliminary efficacy vs confirmatory efficacy) and the need to minimise bias and confounds. Throughout the clinical development process, the perspectives of researchers, ethicists, and patients must be considered, and risks should be minimised whenever possible in a manner that is consistent with good trial design.