This paper presents results of the only large-scale study carried-out in Poland to date on the prevalence of psychopathic traits and their relationship with aggressive behaviour in mainstream adolescents. The sample consists of 9,415 students (4,808 boys, 4,607 girls) in the first to third grades at 142 public secondary schools. Psychopathic traits were measured by teacher-report ratings with the antisocial process screening device (APSD), while aggressive behaviours were assessed using the Reactive-Proactive Aggression Questionnaire. Analysis of results revealed that boys scored much higher than girls in total APSD scale measuring psychopathic traits. Only 2.68% of assessed adolescents scored above the cut-off of 25 points. Results also showed significant correlations between psychopathic traits and both proactive and reactive aggression. The authors concluded that screening a large sample to identify children and youths with psychopathic traits has some important advantages but, on the other hand, it is a sensitive undertaking because of the label 'psychopath' can have negative consequences for the subjects.