A randomized trial was conducted comparing 10 individual weekly sessions of cognitive behaviour therapy for panic disorder (PD) with or without agoraphobia with a 10-module self-help program on the Internet. After confirming the PD diagnosis with an in-person structured clinical interview (SCID) 49 participants were randomized. Overall, the results suggest that Internet-administered self-help plus minimal therapist contact via e-mail can be equally effective as traditional individual cognitive behaviour therapy. Composite within-group effect sizes were high in both groups, while the between-group effect size was small (Cohen's d=16). One-year follow-up confirmed the results, with a within-group effect size of Cohen's d=0.80 for the Internet group and d=0.93 for the live group. The results from this study generally provide evidence to support the continued use and development of Internet-distributed self-help programs.