The current study investigated the 18-month stability of self-reported psychopathic traits measured through the Youth Psychopathic traits Inventory–Child Version (YPI-CV) and their concurrent and prospective associations with conduct problems and aggression in a sample of 9–12 year olds (n = 159, 52% boys) from the community. Self-reported psychopathy scores were moderately to highly stable and traits were positively related to conduct problems both concurrently and at follow-up, the latter even after controlling for initial levels of conduct problems. Higher self-reported psychopathic traits were also related to higher reactive, but particularly proactive aggression at follow-up. Finally, children with persistently high levels of psychopathic traits exhibited higher levels of conduct problems and proactive aggression at follow-up than those with unstable or stable low psychopathic traits.