ImportanceBecause of increased suicide rates among Black youth in the past 2 decades, there is a dire need for research on suicidal ideation and risk factors in this population.ObjectiveTo examine the direct and indirect associations between online racial discrimination and suicidal ideation through posttraumatic stress disorder symptoms among Black adolescents living in the US, with consideration of potential differential associations by gender and age.Design, Setting, and ParticipantsThis cross-sectional study used data drawn from the first wave of the National Survey of Critical Digital Literacy. Black adolescents aged 11 to 19 years were selected from a nationally representative probability-based sample. Data were collected from October 2020 to December 2020 and analyzed from August 2021 to October 2021.Main Outcomes and MeasuresHypotheses of the current study were formulated during research design and grounded in empirical literature. The individual online racial discrimination subscale (Online Victimization Scale), the UCLA Child/Adolescent posttraumatic stress disorder Reaction Index for DSM-5, and an item from the second edition of the Children’s Depression Inventory were used to assess constructs. Mediation was assessed through mediation models with path analyses using structural equation modeling.ResultsAmong a total 525 participants, 265 were girls (50.5%) and 251 were boys (47.8%); the mean (SD) age was 14.8 (2.5) years. Findings from structural equation modeling analysis indicated that individual online racial discrimination was associated with posttraumatic stress disorder symptoms (β = 0.49, SE = 0.06, P < .001), and posttraumatic stress disorder symptoms were associated with suicidal ideation (β = 0.51, SE = 0.06, P < .001). Posttraumatic stress disorder was identified as a full mediator between online racial discrimination and suicide (β = 0.25, SE = 0.04, P < .001). No differences by gender or age were found. Furthermore, no significant direct association between online racial discrimination and suicidal ideation was found.Conclusions and RelevanceThis study found an association between individual online racial discrimination and posttraumatic stress disorder symptoms and between posttraumatic stress disorder symptoms and suicidal ideation. These risk factors are important to consider in continuing studies of the cause of suicidal ideation for Black adolescents in the US.