Background: Childhood maltreatment and peer victimization are major risk factors for depression and suicidal behavior. Furthermore, childhood maltreatment increases the risk of peer victimization. Our objective was to distinguish between the contributions of parental maltreatment and peer victimization to the development of mental health problems in young adulthood. Specifically, we tested whether peer victimization alone or in combination with parental maltreatment before 18 years old was associated with anxiety, depression, and suicidal thoughts and behaviors at age 21 years. Methods: We analyzed data collected from questionnaires administered in the i-Share (Internet-based Students' Health ResearchEnterprise) study in France from February 2013 to September 2019 (N = 2271 participants). We performed multinomial and binary logistic regression analyses to assess the single and combined contributions of childhood peer victimization and parental maltreatment to anxiety, depression, and suicidality in adulthood. Results: Nearly one third of students (28.8%) reported at least one mental health problem; 29.8% reported peer victimization alone; 7.5% reported parental maltreatment alone; and 10.3% reported both parental maltreatment and victimization. In multivariate models, compared to participants that did not experience maltreatment or peer victimization, those that experienced peer victimization alone were more likely to report anxiety (adjusted odds ratio [aOR]: 1.90; 95% CI: 1.50-2.40), depression (aOR: 1.95; 95% CI: 1.46-2.60), or suicidal ideation, without (aOR: 1.62; 95% CI: 1.26-2.09) or with a suicide attempt (aOR: 2.70; 95% CI: 1.51-4.85). Similar associations were observed for participants that experienced maltreatment alone. Participants that experienced both maltreatment and peer victimization were at increased risk of depression (aOR: 2.63; 95% CI: 1.79-3.86) and suicidal ideation, with (aOR: 9.19; 95% CI: 4.98-16.92) and without a suicide attempt (aOR: 2.64; 95% CI: 1.86-3.76).