BACKGROUND: Little is known about the best ways for a member of the public to respond when someone in their social network develops a mental disorder. Controlled trials are not feasible in this area, so expert consensus may be the best guide. METHODS: To assess expert views, postal surveys were carried out with Australian GPs, psychiatrists and psychologists listed on professional registers and with mental health nurses who were members of a professional college. These professionals were asked to rate the helpfulness of 10 potential first aid strategies for young people with one of four disorders: depression, depression with alcohol misuse, social phobia and psychosis. Data were obtained from 470 GPs, 591 psychiatrists, 736 psychologists and 522 mental health nurses, with respective response rates of 24%, 35%, 40% and 32%. Data on public views were available from an earlier telephone survey of 3746 Australian youth aged 12-25 years and 2005 of their parents, which included questions about the same strategies. RESULTS: A clear majority across the four professions believed in the helpfulness of listening to the person, suggesting professional help-seeking, making an appointment for the person to see a GP and asking about suicidal feelings. There was also a clear majority believing in the harmfulness of ignoring the person, suggesting use of alcohol to cope, and talking to them firmly. Compared to health professionals, young people and their parents were less likely to believe that asking about suicidal feelings would be helpful and more likely to believe it would be harmful. They were also less likely to believe that talking to the person firmly would be harmful. CONCLUSION: Several first aid strategies can be recommended to the public based on agreement of clinicians about their likely helpfulness. In particular, there needs to be greater public awareness of the helpfulness of asking a young person with a mental health problem about suicidal feelings.