Intolerance of uncertainty (IU) has been proposed as a transdiagnostic risk and maintenance factor underlying various forms of psychopathology. Few studies, however, have examined IU in hoarding disorder (HD)-a condition characterized by excessive urges to acquire and difficulties discarding possessions-core symptoms that may be fueled by inflated IU. We examined cross-sectional relationships between IU and different symptom facets of HD, controlling for anxiety and depression severity, and explored whether pre-treatment levels of IU predicted response to exposure-based treatment for HD.Fifty-seven individuals seeking treatment for HD completed baseline measures of hoarding symptoms, IU, anxiety and depression. Participants then completed 26 sessions of group exposure-based treatment for HD with or without compensatory cognitive training. Hoarding symptoms were assessed following the final treatment session to index treatment response.IU was positively and significantly associated with greater urges to acquire and greater difficulties discarding possessions, beyond shared variance accounted for by anxiety and depression. IU was not significantly related to clutter symptom severity. Higher pre-treatment IU predicted increased odds of treatment non-response.Elevated IU is associated with specific hoarding symptom clusters and may be an important target for HD treatment.