Although internet-based cognitive behaviour therapy (ICBT) is an effective treatment for social anxiety disorder (SAD), a substantial proportion of patients do not achieve clinically significant improvement. More research is needed to identify which factors predict treatment adherence and outcomes.

The aims of this study were to (1) identify demographic and clinical factors associated with treatment adherence and outcomes in ICBT for social anxiety in China, and (2) explore whether low-intensity therapist support results in improved treatment adherence or outcomes.

Participants were assigned to either therapist-guided (N = 183) or self-guided ICBT (N = 72). Level of social anxiety was measured at both pre- and post-treatment. Treatment adherence and outcomes were analysed using a two-step linear and logistic regression approach. Clinical and demographic characteristics were examined.

No significant group differences were found for treatment adherence or outcomes between the therapist-guided and self-guided conditions. Participants diagnosed with SAD were significantly less likely to drop out (OR 0.531, p = .03) compared with subclinical participants with social anxiety symptoms. Older participants (B = 0.17, SE = 0.04, p = .008) and participants with a diagnosis of SAD (B = 0.16, SE = 0.44, p = .01) tended to complete more modules. Participants who completed more modules (B = 0.24, SE = 0.03, p = .01) and participants who identified as female (B = –0.20, SE = 0.18, p = .04) reported greater reductions in SAD symptoms.

Understanding of factors related to adherence and outcome is necessary to prevent drop-out and optimize outcome.