Recent research suggests that transgender and/or gender nonconforming (TGNC) youth present with heightened levels of mental health problems compared to peers. This study seeks to examine the mental health needs of a large sample of treatment-seeking TGNC youth by comparing them to cisgender males and females. Participants were 94,804 children and youth ages 4–18 years (M = 12.1, SD = 3.72) who completed the interRAI Child and Youth Mental Health Instrument (ChYMH) or Screener (ChYMH-S) at participating mental health agencies in the Ontario, Canada. Overall, the mental health presentations of TGNC youth were similar to cisgender females but at higher acuity levels. TGNC youth showed significantly higher levels of anxiety, depression, social disengagement, positive symptoms, risk of suicide/self-harm, and were more likely to report experiencing emotional abuse, past suicide attempts, and a less strong, supportive family relationship than cisgender females and males. Clinical implications of these findings are discussed.