The study experimentally manipulated self-imagery in highly socially anxious adolescents and found that holding a negative self-image in mind increased anxiety, led participants to believe they performed more poorly, and caused them to overestimate how anxious they appeared to others. Negative imagery also had observable effects on social interactions, with conversation partners and independent observers rating participants as more anxious and less socially effective. Preliminary analyses suggested that these effects may be partly explained by increased use of avoidant safety behaviours. Overall, the findings provide strong support for a causal role of negative self-imagery in adolescent social anxiety and highlight imagery-focused techniques as promising intervention targets.