Posthumous medical data donation (PMDD) for the purpose of legitimate, non-commercial and, potentially, very beneficial medical research has been sparsely discussed in legal scholarship to date. Conversely, quite an extensive social science and humanities research establishes benefits of this practice. It also finds that PMDD enables individuals to employ their altruistic motivations and aspirations by helping them participate in ‘citizen’s science’ and medical research, thus supporting efforts in finding cures for some of the acutest diseases of today. There appears to be no jurisdiction where a regulatory framework supports and enables PMDD. This paper analyses whether and to what extent law and policy should enable this practice. We take a comparative approach, examining the position under both US and UK law, providing the first comparative legal account of this practice. We do not aim to suggest a detailed legal solution for PMDD, but rather key considerations and principles for legislative/policy reforms, which would support the practice of PMDD. We discuss organ donation and provide a comparative outlook with the aim of drawing lessons from this practice, and applying them to the regulation of PMDD. Our analysis is both normative and black letter since we consider arguments regarding the necessity of organ and data donation, as well as the law that regulates these practices.