Mentally ill people are among the most stigmatized, discriminated against and marginalized society members. The aims of this study were to explore adolescents' opinions about mental illness and determine whether these change after a mental health educational intervention. Two randomly selected schools took part in this study: one serving as intervention group and one as comparison group. Data were collected from both groups, before and after the intervention, using the Opinion about Mental Illness scale. Social Discrimination decreased significantly at the post-test in both groups. Score on Social Care factor significantly increased in the intervention group, and the overall change from pre-post to post-test period was significantly different between the groups. Social Integration significantly increased in the intervention group. A significant interaction effect was found indicating that the overall change was different between the two study groups. Thus, mental health educational interventions can positively influence the perceptions towards mental illness among adolescents.