The British National Institute for Health and Clinical Excellence (NICE) has recently (28 January 2009) released new guidelines for the diagnosis, treatment and prevention of the psychiatric category antisocial personality disorder (ASPD). Evident in these recommendations is a broader ambiguity regarding the ontology of ASPD. Although, perhaps, a mundane feature of much of medicine, in this case, ontological uncertainty has significant ethical implications as a product of the profound consequences for an individual categorised with this disorder. This paper argues that in refraining from emphasising uncertainty, NICE risks reifying a controversial category. This is particularly problematical given that the guidelines recommend the identification of individuals "at risk" of raising antisocial children. Although this paper does not argue that NICE is "wrong" in any of its recommendations, more emphasis should have been placed on discussions of the ethical implications of diagnosis and treatment, especially given the multiple uncertainties associated with ASPD. It is proposed that these important issues be examined in more detail in revisions of existing NICE recommendations, and be included in upcoming guidance. This paper thus raises key questions regarding the place and role of ethics within the current and future remit of NICE.