Purpose – Police officers are frequently confronted with moral dilemmas in the course of their job. The authors assume new police officers need guidance, and need to be taught at the police academy how to deal with these situations. The purpose of this paper is to obtain insight into the impact of socialization on police recruits’ knowledge of the code of ethics and their moral reasoning skills. Design/methodology/approach – The study applied a longitudinal mixed methods design, using two methods. The first method was a qualitative observation of integrity training sessions at five police academies in Belgium. The second method was a quantitative survey-measurement of recruits’ knowledge of the code of ethics and their moral reasoning skills at three points in time: the beginning of their theoretical training, before their field training and afterwards. Findings – The analyses show differences between the police academies in their integrity training sessions. Some of these differences are reflected in different levels of knowledge of the code of ethics. As for the development pattern of recruits’ moral reasoning skills, the study found almost no differences between the academies. Perhaps this is because recruits already have relatively high scores when they start, leaving little room for improvement during the one year training program. This suggests an important role of the police selection procedure. Originality/value – Previous research on socialization and police culture has focussed on recruits being socialized in a negative police culture where misconduct is learned. This is a negative interpretation of police integrity. A positive one refers to ethical decision making generally, and moral reasoning specifically. The impact of the socialization process on recruits’ moral reasoning is empirically understudied.