Research has shown that children displaying conduct problems (CP) early in life are at greater risk for severe CP and other negative outcomes later in life. However, not all children with early-onset CP will develop severe CP over the life-course. Thus, it is important to identify those at greater risk, preferably as early as possible, in order to adequately prevent a negative development. Psychopathic traits have received much attention in research on risk for severe CP, involving attempts to extend these traits, and their association to CP to childhood. However, research has thus far mainly focused on one dimension of psychopathic traits, that is callousunemotional (CU) traits, to some extent neglecting two other dimensions of traits commonly included in a psychopathic personality: an interpersonal, and a behavioural dimension. Hence, we still do not know if a full psychopathic personality is identifiable in early childhood, and if and how it is related to the development of severe and persistent CP. The aim of this dissertation was to examine if a psychopathic personality could be identified in early childhood, if psychopathic traits are stable over time, and if and how the psychopathic personality is related to childhood CP. Overall, the results show that psychopathic traits, as well as the display of a psychopathic personality, could be identified in early childhood. These traits were stable over time, and they were clearly and strongly related to childhood CP. Additionally, the combination of early-onset CP and a full psychopathic personality seems to be the most precarious for severe and persistent CP, even more so than the combination of CP and CU traits. With careful consideration to ethical aspects, these results are discussed both in relation to a developmental psychopathology perspective on CP, as well as in relation to diagnostic practice as it is framed today.