Objective Guided Internet‐based cognitive behaviour therapy (ICBT) for panic disorder has been shown to be efficacious in several randomized controlled trials. However, the effectiveness of the treatment when delivered within routine psychiatric care has not been studied. The aim of this study was to investigate the effectiveness of ICBT for panic disorder within the context of routine psychiatric care. Method We conducted a cohort study investigating all patients (n = 570) who had received guided ICBT for panic disorder between 2007 and 2012 in a routine care setting at an out‐patient psychiatric clinic providing Internet‐based treatment. The primary outcome measure was the Panic Disorder Severity Scale‐Self‐report (PDSS‐SR). Results Participants made large improvements from screening and pretreatment assessments to posttreatment (Cohen's d range on the PDSS‐SR = 1.07–1.55). Improvements were sustained at 6‐month follow‐up. Conclusion This study suggests that ICBT for panic disorder is as effective when delivered in a routine care context as in the previously published randomized controlled trials.