Cognitive–behavioral therapy is a well-established treatment for obsessive–compulsive disorder (OCD). There are a variety of cognitive and behavioral strategies, and it is necessary to analyze the outcomes of the treatments. The aim of the present study is to verify the effectiveness of a treatment that combines evidence-based procedures and specific cognitive interventions highlighting the issue of acceptance. Forty patients with OCD were recruited and underwent a specific treatment procedure. All patients had a psychodiagnostic assessment for OCD using the Y–BOCS (Yale–Brown obsessive–compulsive scale) performed twice: before treatment (t0) and after nine months (t1). Data analysis showed a decrease in the scores between t0 and t1 according to the Y–BOCS in terms of the interference, severity, and impairment of obsessive–compulsive symptoms. A repeated-measures ANOVA showed a significant reduction in symptoms after treatment, with values of F (1, 39) = 137.56, p < 0.001, and η2 = 0.78. The ANOVA results were corroborated by a Wilcoxon signed-rank test. A reliable change index analysis indicated that 33 participants reported improvements in symptoms, of which 23 were clinically significant. The results showed clinical relevance for OCD treatment and highlighted how this cognitive procedure favored positive outcomes.