In the cases of Berlioz (2017) and Donnellan (2018), the European Court of Justice has required national judges, under certain conditions, to carry out the transnational judicial review of preparatory acts adopted, in mutual assistance procedures in the tax field, by authorities of EU Member States different from those in which the judiciary concerned is located. The present Article takes an Italian ruling on a case presenting a factual setting similar with Donnellan as a case study, and explores the limits and prospects of such doctrine of transnational judicial review under EU fundamental rights law (with a view, in particular but not exclusively, to the right to an effective judicial remedy). It thus strives to develop a general theory of transnational judicial review for EU administrative law.