Youths are important sources of first aid for people close to them who are experiencing mental health problems, but their skills are not optimal. A better understanding of predictors of young people s first aid intentions and beliefs will facilitate future efforts to improve their mental health first aid skills. Methods: Young people s first aid intentions and beliefs were assessed by a national telephone survey of 3746 Australian youth aged 12-25 years in 2006. A similar survey was repeated in 2011 with 3021 youths aged 15-25 years. In both surveys, youths were presented with a vignette portraying depression, psychosis, social phobia, or depression with alcohol misuse in a young person. The 2011 survey also included depression with suicidal thoughts and post-traumatic stress disorder. Respondents reported on any past-year experience of mental health problems and treatment, exposure to beyondblue and mental health information at school or work. Results: The potential value of encouraging professional treatment was not universally recognized, although young people were mostly aware of and reported the intention to take supportive actions. Respondent age, sex, experience of mental health problems, type of mental disorder, and exposure to mental health information at school, work, or beyondblue all predicted some intentions and beliefs. Some improvements in beliefs were observed between surveys. Limitations: Actual first aid actions and their helpfulness were not measured. Conclusions: Future efforts should target adolescents, males and those with recent mental health problems who had not received help. Beyondblue and school and work settings may be promising avenues for these efforts.