The therapist's self-disclosure (TSD) interventions are considered beneficial and often used by psychotherapists. However, their use remains controversial for several reasons, including the use of broad definitions neglecting the distinction between the TSD and the therapist's self-involving (TSI) interventions. The TSD interventions involve the revelation of personal information to the patient, while the TSI implicates the direct expressions of the therapist's reaction to the patient's statements and behaviors within the session. To compare the immediate therapeutic effects of the TSD and TSI interventions, we conducted a study on 57 total interventions (i.e., 35 TSI and 22 TSD, respectively) performed during 17 psychotherapy sessions in a sample of 6 patients, evaluating the effects of each intervention (TSD or TSI) based on two parameters: patient's cooperative attunement and patient's metacognitive functioning. Results show that, compared to the TSD, the TSI interventions were followed by a higher cooperative attitude and metacognitive functioning of the patients. The difference in the short-term effects of these two interventions suggests the usefulness of considering TSD and TSI distinctly to evaluate their psychotherapeutic effectiveness.