Objective: Although most people will experience a traumatic event at some point in their life, only some will develop significant psychological symptoms in the aftermath. In the current study, we use a preexisting longitudinal study located in Long Island to examine the impact of Hurricane Sandy on internalizing symptoms in a large sample of children, We focused on temperamental fear and a biomarker of risk for anxiety, the error-related negativity (ERN). The ERN is a negative deflection in the event-related potential (ERP) occurring when individuals make mistakes and is increased in anxious individuals. Method: The final sample consisted of 223 children who had undergone an observational assessment of fear at age 3 years and an electroencephalogram assessment of the ERN at age 6 years. At the age 9 year assessment, internalizing symptoms were assessed, and then again after the hurricane (-65 weeks later). Results: A significant three-way interaction among fearfulness, hurricane stressors, and the ERN in predicting posthurricane increases in internalizing symptoms suggested that children who were high in fear at age 3 years and experienced elevated hurricane stressors were characterized by subsequent increases in internalizing symptoms, but only when they were also characterized by an increased ERN at age 6 years. Conclusion: These findings support a diathesis stress model, suggesting that early temperament and prestressor biological markers confer risk for increased psychological symptoms following environmental stressors.