BACKGROUND: Patients who require a switch in their antidepressant therapy may have different clinical profiles and treatment needs compared with patients initiating or maintaining a first-line antidepressant therapy. METHODS: The Prospective Epidemiological Research on Functioning Outcomes Related to Major depressive disorder (MDD) (PERFORM) study was a 2-year observational cohort study in outpatients with MDD in five European countries. Enrolled patients were either initiating or undergoing the first switch to an antidepressant monotherapy. Baseline data on patients' clinical status, functioning, productivity, quality of life and medical-resource use were compared in a cross-sectional baseline analysis. RESULTS: A total of 1402 patients were enrolled, of whom 1159 (82.7%) provided analysable baseline data. The majority (78.7%) of the analysable population were initiating antidepressant treatment and most (83.6%) were enrolled and followed up by general practitioners. Compared with patients initiating antidepressants, those switching antidepressants (21.3%) tended to have more severe depressive symptoms, greater anxiety, worse health-related quality of life, greater functional impairment, greater medical-resource use and had a different medical history. Limitations included an over-representation of switches due to lack of efficacy among patients who were switching treatment, as patients were selected based on presence of depressive symptoms. CONCLUSIONS: Patients with MDD who are switching treatment for the first time have a different profile and different depression-associated health needs compared with those initiating treatment. Therapeutic management should therefore be adapted for patients who switch. TRIAL REGISTRATION: ClinicalTrials.gov NCT01427439 ; Retrospectively registered 26 August 2011.