This study investigated whether implicit attitude (IA) and implicit self-concept (ISC) towards transgression predicted daily-life antisocial behaviour (ASB) in institutionalized adolescents. Eighty-seven adolescents completed two Implicit Association Tests (IAT) assessing IA and ISC towards transgression, and reported four times a day during eight days the intensity of their ASB. Staff members concurrently reported the intensity of each adolescent’s ASB. Adolescents filled in the Inventory for Callous-Unemotional Traits and answered a semi-structured interview assessing conduct disorder. Multilevel regression analyses confirmed that adolescents’ ISC towards transgression significantly predicted their self - and staff-reported ASB over and above conduct disorder and callous-unemotional traits. However, adolescents’ IA towards transgression did not predict their ASB. Results indicate that ISC towards transgression is a reliable predictor of daily-life ASB in institutionalized adolescents. These results suggest that transgression-related ISC represents a promising target for ASB prevention in institutionalized adolescents.