Background <p>Treatment readiness factors, such as treatment credibility and expectancy, are postulated to be predictors of outcomes within the context of cognitive behavioral therapy (CBT). Concentrated exposure therapy (cET) is a form of short-term, intensive, exposure-based CBT that has shown promising results. This study investigated whether treatment expectancy and credibility predict cET treatment outcomes in patients with difficult-to-treat (nonresponders and patients with relapse following CBT) obsessive-compulsive disorder (OCD).</p> Methods <p>A total of 163 patients underwent 4 days of cET treatment. Treatment credibility and expectancy were measured using the Credibility/Expectancy Questionnaire (CEQ) prior to the start of treatment. OCD symptom severity was measured using the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) at pretreatment, posttreatment, 3-month follow-up, and 1-year follow-up. Work- and social functioning were measured before treatment and at the 1-year follow-up.</p> Results <p>Higher CEQ scores were significantly associated with lower Y-BOCS score at posttreatment and follow-up after controlling for age, sex, and pretreatment OCD, anxiety, and depression levels. The CEQ scores were also significantly associated with work- and social functioning at the 1-year follow-up. A receiver operating characteristic analysis suggested a mean item cutoff point of 92.5 (0-100 scale) for the CEQ, and 87% of the patients classified as having high expectancy had a positive treatment response.</p> Conclusions <p>This study confirmed that treatment expectancy and credibility are predictors of cET outcomes in patients with OCD. Higher scores on the CEQ were linked to better treatment results, both immediately and up to one year later. These insights highlight the need to consider patients’ attitudes toward treatment in the early treatment phase.</p> Trial registration <p>ClinicalTrials.gov identifier: NCT02656342 (First registered: 2015-11-30).</p>