This randomized clinical trial aimed to evaluate the clinical efficacy of short-term psychodynamic psychotherapy (STPP) in the treatment of patients suffering from anxiety or depressive disorders, as compared with a control case sample composed of patients undergoing treatment as usual (TAU). Sixty patients with depressive or anxiety disorders according to DSM IV-TR were randomly assigned in a 1:1 ratio to an intervention group (STPP) or control group for 12 months (T1). Primary outcome measures were the Symptom Checklist 90-Revised (SCL-90-R), the Inventory of Interpersonal Problems (IIP), and the Clinical Global Impression Improvement Scale. Intention to treat analysis revealed that patients who received STPP showed significantly more improvements in comparison with those who were in the TAU group on Clinical Global Impression Improvement Scale and IIP measures. This study offers evidence that STPP is an effective treatment for patients with anxiety or depressive disorders, and it could be more effective than TAU in improving interpersonal problems as measured by IIP.