Disorder-specific (DS-CBT) and transdiagnostic (TD-CBT) cognitive behaviour therapy have both been used to treat social anxiety disorder (SAD). This study compared internet-delivered DS-CBT and TD-CBT for SAD across clinician-guided (CG-CBT) and self-guided (SG-CBT) formats. Participants with SAD (n=233) were randomly allocated to receive internet-delivered TD-CBT or DS-CBT and CG-CBT or SG-CBT. Large reductions in symptoms of SAD (Cohen's d≥1.01; avg. reduction≥30%) and moderate-to-large reductions in symptoms of comorbid depression (Cohen's d≥1.25; avg. reduction≥39%), generalised anxiety disorder (Cohen's d≥0.86; avg. reduction≥36%) and panic disorder (Cohen's d≥0.53; avg. reduction≥25%) were found immediately post-treatment and were maintained or further improved to 24-month follow-up. No marked differences were observed between TD-CBT and DS-CBT or CG-CBT and SG-CBT highlighting the potential of each for the treatment of SAD and comorbid disorders. ; 15 page(s)