The picture of adolescence and deception becomes all the more cloudy when the psychopathology of young people is contemplated. In Chapter 4 we considered the ways in which young people present their accounts within the environment of the criminal justice system. In this chapter, we move on to focus on mental health aspects, speci®cally those ``disorders'' that are relevant to the general assessment of adolescents including those who become involved in criminal activity and the associated deceptive communication and challenging interactions that may occur. It is important to emphasize at the start that this chapter refers to a speci®c group of young people and a clear differentiation should be made between those with disorders and those with other challenging behaviours. In fact, care should be taken to separate those without disorders but who display challenging behaviour from those with the disorders covered in the current chapter. It is anticipated that the information presented here will assist practitioners in making these distinctions.