--- - |2+ Background Group cognitive–behavioural therapy (G‐CBT) for hoarding disorder (HD) may be an intervention of choice, considering its efficacy, low costs, and impact on comorbid anxiety and depression. But although G‐CBT and modifications of G‐CBT have been applied, none has assessed G‐CBT efficacy at follow‐up. In the current open‐label pilot study, we tested the efficacy of G‐CBT at posttreatment and 6‐month follow‐up and whether the inclusion of targeted reasoning and self‐identity components added to G‐CBT efficacy. Methods Participants (n = 16) with the HD according to the DSM‐5 criteria without major comorbid conditions and not requiring immediate medical intervention were retained. The intervention included a 20‐week G‐CBT with the inclusion of modules on reasoning and self‐identity. Results Very large/large effect sizes, depending on the outcome measure, were observed at posttreatment. Also, HD severity decreased from posttreatment to 6‐month follow‐up. All participants showed reliable change from pretreatment to follow‐up. Conclusions The results emphasize the efficacy of G‐CBT with additional targeted reasoning and self‐components. - Clinical Psychology & Psychotherapy, Volume 25, Issue 5, Page 701-709, September/October 2018.