Internet-delivered self-help programmes with added therapist guidance have shown efficacy in social anxiety disorder, but unguided self-help has been insufficiently studied. To evaluate the efficacy of guided and unguided self-help for social anxiety disorder. Participants followed a cognitive-behavioural self-help programme in the form of either pure bibliotherapy or an internet-based treatment with therapist guidance and online group discussions. A subsequent trial was conducted to evaluate treatment specificity. Participants (n = 235) were randomised to one of three conditions in the first trial, or one of four conditions in the second. Pure bibliotherapy and the internet-based treatment were better than waiting list on measures of social anxiety, general anxiety, depression and quality of life. The internet-based therapy had the highest effect sizes, but directly comparable effects were noted for bibliotherapy augmented with online group discussions. Gains were well maintained a year later. Unguided self-help through bibliotherapy can produce enduring improvement for individuals with social anxiety disorder.