OBJECTIVE: To determine the mental health first-aid knowledge and beliefs of young people and their parents. METHODS: A national telephone survey was carried out with 3746 people aged 12-25 years. Interviews were also carried out with 2005 co-resident parents. First-aid knowledge was assessed in response to one of four randomly presented vignettes covering depression, depression with alcohol misuse, social phobia and psychosis (schizophrenia). Young people were asked about first aid in relation to a peer and parents in relation to a child. RESULTS: The potential value of encouraging professional help-seeking was not universally recognized by either young people or adults. In general, positive social interactions were endorsed as likely to be helpful and negative ones as not, but again there is considerable room for improvement. Adolescents had less sophisticated first-aid knowledge and beliefs than young adults, but were paradoxically more confident about providing help to a peer. CONCLUSIONS: These findings show that there is a continuing need for further community education about the potential benefits of early professional treatment of young people developing mental disorders.