More than 11% of Scots had tried to take their own life by the age of 35 and 16% had self-harmed, according to researchers.
The study, led by the University of Glasgow, involved 3 508 participants from Scotland, which has some of the highest suicide rates in the UK.
It is the first to have focused on the prevalence of incidents in 18 to 34 year olds.
Lead author Professor Rory O’Connor said: “These results are stark, and serve to highlight the scale of suicide attempts and self-harm in our country’s young people.”
Mental healthy charity SANE said the figures were “shocking” and showed support services needed to be “more effective and responsive”. The study appears in the BJPsych Open journal.