BACKGROUND: Past studies have demonstrated better mental health and well-being among transgender youth who had accessed gender-affirming care. However, few existing studies have assessed unmet need for gender-affirming care as a social determinant of mental health inequities. METHODS: Data on unmet need for gender-affirming care, distress and suicidality were analysed from the 2018 Counting Ourselves nationwide community-based survey of transgender people in Aotearoa/New Zealand. Associations between unmet need for gender-affirming care and mental health indicators were tested for transgender youth within the sample (aged 14-26 years; n = 608; Mage = 20.5). RESULTS: Transgender youth reported unmet needs ranging from 42% for gender-affirming hormone to 100% for feminizing surgeries and voice surgeries. Overall unmet need for gender-affirming care was associated with worse mental health. Trans men with an unmet need for chest reconstruction (84%) scored an average of 7.13 points higher on the K10 Psychological Distress Scale relative to those whose need had been met. Participants reporting unmet need for hormones (42%) had twice the odds (adjusted odds ratios = 2.01; CI = 1.02-3.98) of having attempted suicide in the last 12 months. CONCLUSIONS: Dismantling barriers to accessing gender-affirming care could play a crucial role in reducing mental health inequities faced by transgender youth.