Mood disorders, anxiety, and suicidality in youth are increasing and rapid-acting treatments are urgently needed. One potential is ketamine or its enantiomer esketamine, which was FDA approved in 2019 to treat major depressive disorder with suicidality in adults. This systematic review evaluated the evidence for the clinical use of ketamine to treat mood disorders, anxiety, and suicidality in youth. The PRISMA guidelines were used, and a protocol registered prospectively ( https://osf.io/9ucsg/ ). The literature search included Pubmed/MEDLINE, Ovid/MEDLINE, Scopus, CINAHL, PsychInfo, and Google Scholar. Trial registries and preprint servers were searched, and authors contacted for clarification. Studies reported on the clinical use of ketamine to treat anxiety, depression, bipolar disorder, or suicidality in youth ≤19years old and assessed symptoms before and after ketamine use. Study screening and data extraction were conducted independently by 2-4 authors. Safety, tolerability, and efficacy data were collected. The Cochrane Risk of Bias guidelines assessed the quality of the evidence. Twenty-two published reports based on 16 studies were identified: 7 case studies, 6 observational studies, 3 randomized trials, and 6 secondary data analyses. Studies reported immediate improvements in depression, anxiety, and suicidality. Improvements were maintained for weeks-months following treatment. Ketamine was well-tolerated with the most common side effects being dizziness, nausea, and mild dissociation. Transient hemodynamic changes were reported, all of which resolved quickly and did not require medical intervention. Initial evidence suggests ketamine is safe and may be effective for mood disorders, anxiety, and suicidality in youth. Further randomized trials are warranted.