How can we understand the troubling under-inclusiveness of our law of mental disorder – its failure to recognize mental conditions that, on the most compelling theoretical accounts of how mental disorder operates on criminal responsibility, ought to concern us deeply? This article argues that the gap between our plausible theories of criminal responsibility and our practices relating to mental disorder is best understood as a marker for the criminal law’s central social function: the laundering and containment of blame. The article begins by canvassing the conceptual structure of the defence of mental disorder, turning then to the troubling prevalence of mental disorder among those facing criminal judgment, looking specifically at the incidence and effects of FASD, autism spectrum disorder, and anti-social personality disorder. These conditions operate on key elements of our theoretical account of criminal responsibility but are excluded from our defence of mental disorder. Yet giving serious doctrinal regard to facts about mental disorder that ought to be of theoretical concern would destabilize individual responsibility for crime, showing itself as a far more complex social and political matter than we like to admit and raising questions about our collective standing to blame. The article argues that this analysis gives a line of sight into the symbolic and communicative role of the law of mental disorder, and the criminal law more generally – it is a mechanism for the concealment of collective responsibility for complex social problems.