Finland register study — Ruuska et al. 2026

Finland followed every person under 23 who contacted a specialist gender clinic from 1996 to 2019 — 2,083 people — and compared them with 16,643 matched peers in official records. Serious psychiatric illness was already much more common before referral. It did not fade after hormones or surgery.

• Before referral, about 46% already had serious psychiatric illness, versus about 15% of matched peers. Two or more years later it was about 62% versus about 15%.
• People referred after 2010 had even greater psychiatric need than earlier cohorts.
• Among those who received sex-rejecting hormones or surgery, psychiatric illness rose over follow-up — about 10% to 61% in feminising treatment, and about 22% to 55% in masculinising treatment.
• After prior psychiatric treatment was counted, referred youth still had about three times the psychiatric-illness risk of female peers and about five times that of male peers.
• The authors: psychiatric needs do not subside after medical transition.