To the Editor: Approximately one-third of patients with major depressive disorder (MDD) are treatment resistant. 1,2 Despite high prevalence, the clinical characteristics and management of treatment-resistant depression (TRD) are not well described. We present a comprehensive clinical description of a case series of 79 well-characterized patients with TRD referred to a university-based TRD specialty clinic.Method. Of 104 patients referred to our TRD clinic from 2009 to 2014, 79 met clinic inclusion criteria: DSM-IV-TR-defined MDD with resistance to ≥ 3 antidepressant trials of adequate dose and duration and no diagnoses of bipolar I or II disorder, personality disorder, psychotic disorder, or alcohol or drug abuse/dependence. Medical records for psychiatric treatments within at least 5 years were obtained. Psychiatric history, including symptom, clinical, family, and treatment information, was obtained at the initial visit. Patients completed the Montgomery-Asberg Depression Rating Scale (MADRS). 3 Institutional review board approval and patient consent were obtained for research use of data.Results. Of the 79 patients, 67% (n = 53) were women; the mean age was 49.3 years (SD = 14.2). One-third (n = 26) were receiving disability support. The mean age at MDD onset was 24.3 years (SD = 13.8), with 50% of patients reporting MDD onset after age 18. The mean number of lifetime MDD episodes was 2.6 (SD = 1.7), with 70% (n = 55) of patients reporting ≥ 2 episodes; 30% (n = 24) reported 1 sustained MDD episode. The mean number of lifetime MDD years was 18.6 (SD = 10.0), with 51% (n = 40) of patients reporting ≥ 18 years. Most patients, 63% (n = 50), reported at least 1 psychiatric hospitalization; 21% (n = 17) reported ≥ 4 hospitalizations (maximum = 20). Of those hospitalized at least once, the mean number of hospitalizations was 3.8 (SD = 4.3); 43% (n = 34) of all patients reported ≥ 2 hospitalizations. At least 1