In a variety of jurisdiction, legislation regarding mental health provides that a criterion of dangerousness must be taken into account when considering the involuntary psychiatric commitment of an individual. In the first section of this article, the author will discuss the context leading to the adoption of the dangerousness criterion as a justification of an involuntary psychiatric commitment. In section 2, the author will identify epistemological obstables, notably the (in)capacity of psychiatry in establishing the futur risk of dangerousness in a patient. Finally, in section 3, the author will evaluate the means by which the dangerousness criterion is applied to children and youth, while raising the risks of adopting an abnormality norm when pedopsychiatric evaluations of the state of children and youth take place.