Cognitive behavioural therapy (CBT) for problematic hoarding is an effective treatment, but further research in diverse, naturalistic settings is needed to see whether this treatment is effective across settings and in smaller doses. The current study investigated the outcome of a 12-session group CBT for hoarding offered in an outpatient hospital setting. Sixty-four participants completed therapy, and 38 participants completed posttreatment assessments. Results demonstrated statistically significant improvements in hoarding symptom severity, saving cognitions, and self-reported distress tolerance. Effect sizes for changes in saving cognitions were generally large. However, effect sizes were modest for most other outcome variables, and only 4 of 38 participants achieved clinically significant change in hoarding symptom severity. These results suggest that 12 sessions of group CBT for hoarding is associated with significant change in saving cognitions, but less meaningful change in other indicators of symptom severity.