This work presents a case study in which Cognitive-Integrative psychotherapy was used to treat a patient with obsessive-compulsive disorder with the implementation of routine outcome monitoring (ROM) at Aiglé Foundation in Argentina. The patient, a 34-year-old female with a university degree reports having obsessive ideas about dirt or pollution, causing harm to others, and religious and superstitious topics on a daily basis. The therapeutic process carried out during the first 17 psychotherapy sessions is described: construction of the therapeutic alliance, psychoeducation, and main interventions. The purpose of the article is to describe a case in which the measures’ results did not show clinically relevant improvement even though the clinical indicators assessed by the therapist and the patient’s subjective evaluation were positive. The article, shows the application of ROM during the supervision process, proposes interpretations of these results, and discusses decision-making processes in the light of this discrepancy.