Suicidal ideation increases in adolescence, especially for anxious youth, and is a frequent precursor to suicide. This study examined whether neural processing of social rejection interacted with negative social experiences to predict suicidal ideation. Thus, to our knowledge this is the first study to examine how brain function may interact with the environment to contribute to suicidal ideation in youth, consistent with a developmental psychopathology perspective. Thirty-six anxious youth (ages 11 to 16) completed diagnostic interviews and questionnaires, an ecological momentary assessment (EMA) protocol, and a functional magnetic resonance imaging paradigm. Results showed that youth experienced greater severity of suicidal ideation when they exhibited heightened activation to social rejection in the right anterior insula and also experienced high levels of peer victimization or EMA-measured daily negative social experiences. Findings provide preliminary evidence that alterations in neural processing of social rejection interacts with exposure to negative social experiences to contribute to suicidal ideation.