Sexual minorities experience greater mental health issues compared to heterosexuals due to minority stressors. This study focused on the impact of victimization and neuroticism on mental health in young men who have sex with men (YMSM), and the mediating role of internalized homophobia (IH). IH refers to when a sexual minority person internalizes social bias and develops a negative view of themselves, which is a likely process through which victimization and neuroticism impact mental health. Data were collected over three time points across 12 months, with 450 YMSM (mean age = 18.9) and an 80.7% retention rate. Two mediation analyses with bias-corrected bootstrapping using 1000 samples were conducted, controlling for age, race, and sexual orientation. Results revealed that victimization [F (9, 440) = 4.83, p < .001, R2 = .09] and neuroticism [F (9, 440) = 12.23, p < .001, R2 = .20] had a significant indirect effect on mental health via increased levels of IH. These findings show how external experiences of stigma and personality level characteristics may impact YMSM in terms of their sense of self. Furthermore, these results support addressing social conditions that marginalize YMSM in order to promote better mental health through decreasing IH.