Background and objective: The Good Behaviour Game (GBG) has been shown to be effective in preventing childhood disruptive behaviours and their long-term unfavourable health-related outcomes. Like many other evidence-based preventive health programmes, however, its current use in Dutch primary schools is limited, and knowledge of the factors influencing the adoption of the programme is scarce. This study aimed to provide a theory-based description of the GBG adoption process and to examine factors influencing this process in primary schools in Amsterdam. Design and methods: In this mixed-methods observational study, semi-structured face-to-face interviews with decision makers from schools that did (n = 11), and did not (n = 6), adopt the programme were supplemented with structured telephone interviews with non-adopters (n = 39). Based on Rogers' Diffusion Theory, the qualitative data were analysed using a deductive approach. Results: Factors facilitating the adoption of the GBG were specific school needs and problems, formulated in educational rather than health terms, and the visibility of the programme's positive effects. Factors impeding adoption were competing programmes in schools and being unaware of favourable funding opportunities. In contrast to previous studies, "time investment" did not play an impeding role. Conclusion: Adoption of prevention programmes in schools may benefit from framing dissemination strategies in educational terms, and using self-assessment procedures to reveal specific needs/problems and to create a "readiness to change". In addition, adoption may benefit from using active dissemination strategies, including opinion leaders reporting their positive experiences with the programme, and the termination of any ineffective programmes that schools currently use.