The primary aim is to describe the changes in the knowledge of mental health conditions, the attitudes toward the mentally ill, and the intended behaviour towards people with mental illness among the entire student population of the third year of a degree course in Psychology. A total of 570 students attended a seminar on stigma towards mental illness and were invited to complete an online survey which collected data on sociodemographic characteristics and three validated questionnaires evaluating different aspects of stigma at three different time points (pre-intervention, post-intervention, and at one year follow up). A total of 253 students (44.39%) completed the questionnaires at t0, t1, and t2. The mean age of the sample was 23.7 (SD = ±5.89), and 86.96% (n = 220) were females. Between t0 and t1, a statistically significant improvement was observed for all three outcomes, while the intended behaviour outcome was no longer significant between t1 and t2 (Z = −0.70; p = 0.48). Females and who participated live at the seminar maintained a significant knowledge of mental illness and a better attitude toward community mental health care. The effects of the seminar focused on reducing stigma tended to diminish over time at one year follow-up, particular in relation to intended behaviour.