Mental illness stigma may contribute to suicidality and is associated with social isolation and low self-esteem among young people at risk of psychosis. However, it is unclear whether mental illness stigma contributes to suicidality in this population. We therefore examined the associations of self-labeling and stigma stress with suicidality among young people at risk. Self-labeling as "mentally ill", stigma stress, social isolation, self-esteem, symptoms and suicidal ideation were assessed in 172 individuals at risk of psychosis. Self-labeling and stigma stress were examined as predictors of suicidality by path analysis. Increased self-labeling as "mentally ill" was associated with suicidality, directly as well as indirectly mediated by social isolation. More stigma stress was related to social isolation which in turn was associated with low self-esteem, depression and suicidal ideation. Social isolation fully mediated the link between stigma stress and suicidal ideation. Interventions to reduce the public stigma associated with risk of psychosis as well as programs to facilitate non-stigmatizing awareness of at-risk mental state and to reduce stigma stress among young people at risk of psychosis might strengthen suicide prevention in this population.