Examine change in the magnitude of antidepressant effects as a function of number of TMS sessions and to determine whether extended treatment courses, beyond 30 and beyond 36 TMS sessions, result in improved efficacy.

The efficacy of TMS in major depressive disorder (MDD) has markedly improved since the pivotal sham-controlled trials. While this enhanced efficacy has been attributed to use of longer treatment courses, the impact of number of treatment sessions on efficacy has not been adequately evaluated. The study device is the Neuronetics, Inc. NeuroStar® TMS Therapy System (K160703, K201158).The study is a retrospective analysis of real-world data from commercial centers. The data will be gathered from the Neuronetics database called TrakStar which collects records of each patient's treatment. The data will be used only as applicable to the objectives of this study.

Inclusion Criteria:

1. Male or female.
2. At least 18 years of age.
3. Treatment with NeuroStar TMS Therapy.
4. Treatment date of November 01, 2008 or later.
5. Patient received at least one treatment with NeuroStar TMS Therapy according to standardized NeuroStar TMS Therapy treatment protocols.
6. Primary diagnosis of Major Depressive Disorder (MDD) with no comorbid diagnosis.
7. PHQ-9 scores available at baseline (pre-treatment).
8. Moderate or greater depression prior to the initial treatment course with NeuroStar TMS Therapy, defined as baseline score on the Physician Health Questionnaire-9 (PHQ- 9) ≥ 10.

The study population comprises patients who were treated with Extended NeuroStar TMS Therapy for MDD on or after November 8, 2008, and whose treatment information was entered in the Neuronetics TrakStar registry at one of the qualifying participating study sites, and for whom the pre-specified required data elements are available in the TrakStar registry and who satisfy each of the study inclusion criteria and none of the exclusion criteria.