Fifty-five people with panic disorder (PD) were randomised to internet-based cognitive behavioural panic treatment (CBT) (with email contact), therapist-assisted CBT manual or information-only control (both with telephone contact). Both CBT treatments were more effective in reducing PD symptomatology, panic-related cognition, negative affect, and number of GP visits and improving physical health ratings. Internet treatment was more effective than CBT manual in reducing clinician-rated agoraphobia and number of GP visits at post-assessment. At follow-up, these effects were maintained for both CBT groups, with internet CBT better at improving physical health ratings and reducing GP visits. This study provides support for the efficacy of internet-based CBT.