Background: Most of the studies on the duration of untreated illness (DUI) as a possible predictor of the clinical outcome and the course have focused on the psychotic disorders. The present naturalistic study was aimed to evaluate the possible relationship between the DUI and some clinical characteristics of a sample of patients with major depressive disorder (MDD). Methods: Sixty-eight patients with MDD, according to the Diagnostic and Statistical Manual of Mental Disorders, IV Edition, Text Revision (DSM-IV-TR) criteria, followed-up for 4 years, were selected, interviewed and their clinical charts reviewed. The DUI was defined as the interval between the onset of the first major depressive episode and the first adequate antidepressant treatment. The sample was divided in two groups according to a DUI ≤ 12 months (n = 45) and > 12 months (n = 23). The main demographic and clinical course variables were compared between the two groups using t-tests or chi-squared tests. Results: Patients with a DUI > 12 months were more frequently women (χ2 = 4.005, p = 0.045), had an earlier onset (t = 2.515, p = 0.014), a longer duration of illness (t = -2.483, p = 0.016), a higher number of recurrences (t = -2.262, p = 0.027) and had more frequently comorbid Axis I disorders with onset later than MDD (χ2 = 5.595, p = 0.05). Conclusions: These findings suggest that a longer DUI may negatively influence the clinical course of MDD. Further studies on larger samples are warranted to confirm these preliminary results.
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