In this study conducted in the French-speaking part of Switzerland, 52 individuals with social phobia were randomly assigned either to an Internet-based cognitive-behavioral treatment with minimal contact with therapists via e-mail or to a waiting-list control group. Significant differences between the two groups were found at posttreatment on all primary outcome measures (social anxiety measures) and on two of the secondary outcome measures (general symptomatology, therapy goal attainment). On average, within-groups effect sizes were large for the primary outcomes (Cohen's d=0.82) and for secondary outcomes (Cohen's d=1.04). Moreover, subjects in the treatment group fulfilled the criteria of clinically significant improvement significantly more often than subjects in the control group on all measured dimensions (58% vs. 20%). Users' acceptance of the program was high. The results from the present study lend further support to the hypothesis that Internet-delivered interventions with minimal therapist contact are a promising treatment approach to social phobia.