The negative attitudes surrounding mental disorders and their treatment are a major obstacle to the correct identification and treatment of emerging psychopathologies. The purpose of this study was to investigate mental health literacy in a large and representative sample of high school students in Italy, via a booklet containing several questionnaires delivered to 1032 teenagers. The items in the questionnaires probed knowledge about mental health and illness, stigmatization, stereotypes, behaviors, opinions, and attitudes. In general, the students had a reasonable knowledge of mental disorders and were able to distinguish these from somatic disorders. However, a large portion of the students nourished some misconceptions about mental disorders and was also rather skeptical about the effectiveness of treatment or the chance of recovery for people with severe mental disorders. Nevertheless, roughly half of the students reported being willing to provide help to someone with a mental disorder when in need. Poor mental health literacy is a major barrier to seeking help and receiving effective treatment. Young people are the ideal target of raising awareness and antistigma campaigns because they are at a higher risk for developing a psychopathology.