Elevated responding to safety cues in the context of threat is associated with anxiety disorder onset, but pathways underlying such responding remain unclear. In this study, we examined whether childhood/adolescent adversity was associated with larger startle reflexes during safe phases of a fear-potentiation startle paradigm (following delivery of an aversive stimulus) that predict anxiety disorders. Participants (N = 104) came from the Youth Emotion Project, a longitudinal study of risk factors for emotional disorders. Participants with no baseline psychopathology underwent a startle-modulation protocol and assessment for childhood and adolescent adversities using a validated interview. Adolescent adversity was associated with larger startle reflexes during the safe phases following an aversive stimulus. Neither child adversities nor adolescent adversities were associated with responding during any other phase of the protocol. These findings suggest a pathway between adolescent adversity and a risk factor for anxiety disorders in which adolescent adversity contributes to impaired responding to safety cues.