In some criminal cases a forensic psychiatrist is asked to make an assessment of the state of mind of the defendant at the time of the legally relevant act. A considerable number of people seem to hold that the basis for this assessment is that free will is required for legal responsibility, and that mental disorders can compromise free will. In fact, because of the alleged relationship between the forensic assessment and free will, researchers in forensic psychiatry also consider the complicated metaphysical discussions on free will relevant to the assessment. At the same time, there is concern about the lack of advancement with respect to clarifying the nature of the forensic assessment. In this paper I argue that, even if free will is considered relevant, there may be no need for forensic researchers to engage into metaphysical discussions on free will in order to make significant progress. I will do so, drawing a parallel between the assessment of criminal responsibility on the one hand, and the medical practice of obtaining informed consent on the other. I argue that also with respect to informed consent, free will is considered relevant, or even crucial. This is the parallel. Yet, researchers on informed consent have not entered into metaphysical debates on free will. Meanwhile, research on informed consent has made significant progress. Based on the parallel with respect to free will, and the differences with respect to research, I conclude that researchers on forensic assessment may not have to engage into metaphysical discussions on free will in order to advance our understanding of this psychiatric practice. © 2010 The Author(s).