Aggression in healthcare systems poses a major problem for nurses because they are the most susceptible to suffer violence. Studies demonstrate that attitudes of nurses influence their behaviour regarding aggression and violence. Training programmes can positively change nurses' attitudes. This quasi-experimental study aimed to examine the effects of a systematic training course in aggression management on mental health nurses' attitudes about the reasons for patients' aggression and on its management. Sixty-three nurses (29 in the intervention and 34 in the control group) participated in this quasi-experimental pre-test and post-test study. The attitude of the participants of a training course was recorded by the German version of the Management of Aggression and Violence Attitude Scale (MAVAS). No significant attitude changes occurred in the intervention group at post-test. It is concluded that trainings intending to influence attitudes regarding the reason for patient aggression should consider the impact of the pedagogical quality of the training course, organizational support, and the user's perception. Moreover, it remains questionable to what extent a single instrument of measurement can record attitude changes.