In the wake of deinstitutionalisation, a range of punitive, restrictive and coercive measures for controlling the lives of people with intellectual disabilities have emerged from criminal law. This article critically engages with one of these measures, the Australian state of Victoria s, supervised treatment order (STO) regime. Drawing on STO decisions, this article argues that, during STO tribunal hearings, the margins of criminal and civil law converge, and the margins of law and medicine further conflate such that the medical diagnosis of a person s intellectual disability becomes a legal diagnosis of that person s innate and ongoing risk and danger to society. That is to say, during STO tribunal hearings, the characteristics and features which typically contribute to medical diagnoses of intellectual disability become the characteristics and features which are now used to diagnose the presence of risk and dangerousness in legal subjects. The article explores the implications of these converging diagnoses for our understanding of people with intellectual disabilities engagement with civil and criminal justice systems, the fluid nature of medico-legal boundaries, and the shifting nature of civil and criminal institutional controls over time.