The main aim of this study was to objectify the treatment assignment criteria used in a clinical centre for addiction treatment in Spain. A sample of 162 patients (87 inpatients and 75 outpatients) who sought treatment between 2010 and 2012 was assessed. Clinical characteristics (addiction severity, psychopathological symptoms, impulsiveness and maladjustment) of the two treatment groups (inpatient and outpatient) into which patients were assigned according to the clinical criteria of therapists were analysed to identify which variables were more relevant for patient placement. Moreover, the therapeutic progression of patients who met and did not meet the assignment criteria received was studied. According to the results, a score above 4 in the family/social support area of the European Addiction Severity Index (EuropASI), or, in cases of a score between 2 and 4 in the family/social area of EuropASI, a score above 2 in the partner subscale of the Maladjustment Scale correctly classified 73.5% of cases (96.6% of inpatients and 46.7% of outpatients). Comparisons of therapeutic results depending on matching or mismatching these assignment criteria showed a larger effect size in mismatching patient assignment criteria for outpatient treatment. The results obtained in this study provide an objective criterion for addicted patient placement. Moreover, from a cost-effective perspective, they question the necessity of inpatient treatment in most cases, demonstrating that outpatient treatment is a sufficient level of care. This study addresses the approach to assigning patients to the treatment modality that best fits them, implementing the least expensive level of care needed to achieve treatment success. (C) 2017 Elsevier Inc. All rights reserved.