The aim was to further test the reliability and validity of a newly developed instrument designed to assess psychopathic personality traits in children, the Child Problematic Traits Inventory (CPTI). Data from the Preschool Twin Study in Sweden were used, a national general population study of 5-year-old twins (n = 1,188, 50.3% girls). Both preschool teachers and parents were used as informants. Confirmatory factor analysis replicated the intended three-factorial structure of the 28 items of the CPTI. Overall, our findings demonstrated good internal consistency and convergent validity, with all the teacher-rated CPTI scores being associated with teacher and parent ratings of externalizing psychopathology, aggressive behavior, fearlessness, and prosocial peer involvement. In conclusion, the CPTI hold promise as a teacher-rated tool for assessing psychopathic traits in childhood, though more research is needed to see if these findings can be generalized to other countries, settings, and older children.