Externalising behaviours such as substance misuse (SM) and conduct disorder (CD) symptoms highly co-ocurr in adolescence. While disinhibited personality traits have been consistently linked to externalising behaviours there is evidence that these traits may relate differentially to SM and CD. The current study aimed to assess whether this was the case, after examining the nature of the relationship between SM and CD symptoms in an adolescent sample (N = 392), using structural equation modelling. Similar to those found in adults (Krueger et al. Journal of Abnormal Psychology 116: 645-666, "2007"), results showed that CD and SM symptoms were organized hierarchically, with symptoms explaining a single broad, coherent construct of externalising behaviour, but also explaining specific factors of SM and CD that vary independently from the general externalising factor. Furthermore, disinhibited personality traits related differentially to these factors, with results showing that, even controlling for inhibited personality traits, impulsivity was associated with CD and the common variance shared by CD and SM, while sensation seeking was specifically associated with SM only. Hopelessness was also associated with the common variance shared by SM and CD. Results confirm impulsivity, hopelessness and sensation seeking as key correlates of externalising behaviour problems in adolescence, identifying them as clear targets for intervention and prevention strategies.