There is clear evidence that people who are attracted to the same gender face worse mental health outcomes than their peers; however, it is unclear if this problem is worse at particular stages of development. To clarify this, a systematic review was conducted to describe the overall trajectories of mental health difficulties across development for same-gender attracted youth compared to their peers. The search identified ten studies that examined depressive symptoms, suicidality and eating disorder symptoms. Disparities in these outcomes were evident by the earliest time points recorded and lasted across the full age range of youth under investigation (ages 10–25). There was some evidence that risk of depressive symptoms and suicidality specifically for same-gender attracted youth was greater in both absolute and relative terms during late adolescence. As young people who are attracted to the same gender are vulnerable to mental health problems across their youth, psychological interventions should be developed which target this group across this span. Interventions beginning at least as early as early adolescence may be ideal to help avoid particular elevations in depressive symptoms and suicidality which are evident in late adolescence for this group.