As football clubs are facing different ethical challenges, many clubs are turning to ethical codes to counteract unethical behaviour. However, both in- and outside the sport field, uncertainty remains about the effectiveness of these ethical codes. For the first time, a longitudinal study design was adopted to evaluate code effectiveness. Specifically, a sample of non-professional football clubs formed the subject of our inquiry. Ethical code effectiveness was assessed by the measurement of the ethical climate. A repeated-measurements ANOVA revealed a positive (...) evolution of the ethical climate within the studied football clubs. This evolution could not be ascribed to the mere presence of an ethical code. However, several potential code effectiveness determining characteristics were also included in the research design. Some of these accounted partly for the evolution of the ethical climate of the football clubs. Results suggest that football clubs should incorporate their ethical code into a broader ethical programme, with attention for professionalization initiatives, stakeholder management, ethical leadership, and whistle-blowing protection. (shrink)