Neurocognitive function (NCF) impairment is an important component of primary and metastatic brain tumors and their therapeutic interventions. As a result, modern clinical trials of cranial irradiation for adult cancer patients have incorporated NCF testing as a primary or secondary end point. In doing so, these clinical trials have provided a novel insight into our understanding of the NCF effects of cranial irradiation and brain tumor progression. In this article, we review these clinical trials both in terms of the trial findings and in terms of the types of NCF tests used in these trials. We also provide an introduction to the strengths and limitations of these NCF tests, as well as expert commentary on the current status and future directions of NCF testing in brain tumor trials.