Background: A callous (lack of empathy and guilt) and unemotional (shallow emotions)-(CU)-trait is part of the concept of psychopathy, and it defines a subgroup of disruptive behavior disorders (DBDs), at increased risk for antisocial outcome. We explored implications of psychopathy and CU trait in a school sample and in a clinical sample of youths with DBDs. Methods: 214 students (aged 6 to 14 years) were screened for behavioral disorders with a teacher-rated instrument (Strength and Difficult Questionnaire). The clinical sample included 81 referred youths (age range 6 to 16 years) with DBDs. Results: All measures of psychopathy and CU dimension distinguished the 19 youths screened for behavior disorders from the normal subjects of the school sample. The same measures distinguished the clinical sample from the normal subjects of the school sample, irrespective of the specific diagnosis of DBD (oppositional-defiant disorder or conduct disorder) and co-occurring comorbidities. In the clinical sample the psychopathic and CU traits were not affected by comorbidities. Youths screened in the school sample and referred youths shared most of the psychopathic and CU traits. Conclusions: The psychopathic and CU traits may be a core element of DBDs, both in clinical and non clinical populations, and they may be explored with standardized instruments.