The cross-cultural adaptation of interventions - defined as the deliberate modification of the design or implementation of interventions for a new context - is more resource-efficient than developing new intervention proposals from scratch. However, such adaptation must be approached methodically and evidence-based, as certain modifications, particularly those involving core components, can compromise the original intervention's effectiveness. Based on this premise, we aim to present the process of cross-cultural adaptation and validation of an antibullying intervention program developed in Italy (Notrap!) for use in Brazilian schools. This is a qualitative study encompassing the stages of translation/back-translation, adaptation, and validation of the program. The adaptation process incorporated a cultural sensitivity framework, an ecological validity framework, and principles of cross-cultural evaluation research. To assess aspects such as structure, layout, scope, and appropriateness of the intervention's activities/materials, a two-round Delphi Method was applied. This stage included the participation of four judges (aged 22 to 27), all of whom were enrolled in a Master's program and had research experience on violence. For dialogic assessment of the material by the target audience, four focus group sessions were conducted in a school setting with seven adolescents (aged 15 to 17) who were students at the school. Applying the cultural sensitivity framework revealed the need to incorporate Brazilian cultural expressions into certain sections of the original intervention materials. Both expert judges and the target audience assessed the ecological validity framework, demonstrating a high level of reliability. The qualitative analysis supported the culturally sensitive modifications or additions made to the original program - such as cultural elements and textual translations from Italian - which were considered ecologically valid and representative. This research provides supporting evidence for future quasi-experimental studies aimed at confirming the effectiveness of the Notrap! intervention in Brazilian settings, as has already been observed in Italian schools.