The number of children being referred to specialists because they are distressed about their gender has risen sharply, figures have shown.
Thirty-four children were referred to the Young People's Gender Service in 2013, rising to 150 last year.
Gender equality group Scottish Trans Alliance said the increase was down to increased awareness of trans issues.
But the group has warned the service was under-resourced and waiting times were too long.
The Young People's Gender Service at Sandyford offers a "comprehensive gender identity service" to children concerned about their gender.
It is run by NHS Greater Glasgow and Clyde, but receives referrals from across Scotland. The figures were revealed by The Times Scotland.
Source: Scottish government
James Morton, manager at the Scottish Trans Alliance, said: "I think back in 2013 if you were a young person struggling with gender, they did not know where to turn to.
"And if they went to see their GP, often their GP would not know where to turn to either. But over the last few years, the referral pathways have become much clearer.
"It's also only in the last few years that many children have become aware of a word to describe what they're going through."
The clinic sees people with "gender dysphoria" - when someone experiences discomfort or distress because there is a mismatch between their biological sex and gender identity.
Mr Morton said waiting times at Sandyford were often several months and could be more than a year.
"The staff there are excellent, but the hours they have available to see people are too small," he said.
"NHS Scotland have been trying to expand capacity, but it's a struggle to catch up with demand"
He told the BBC he believed waiting times should be 18 weeks in common with other outpatient clinics, but said that could be achieved with just one more full-time post at the centre.
NHS Greater Glasgow and Clyde said the team at Sandyford had been increased after a "rapid increase" in referrals in 2015 and 2016.
Currently a consultant child psychiatrist, consultant child psychologist, a principal child psychologist, an occupational therapist and a counsellor work at the centre.
The health board said in a statement: "We anticipate that referrals will continue to rise. The service has continued to receive new referrals this year.
"As it remains the only service in Scotland providing specialist care to young people experiencing issues with their gender identity, it is an essential component part of NHS services in Scotland."