OBJECTIVES: Anxiety is frequently associated with major depressive disorder (MDD). Antidepressants are approved for MDD and some anxiety disorders. However, few data exist on real-life utilisation and outcomes of antidepressant treatments in patients with MDD and co-morbid anxiety. This study aims at describing and comparing treatment patterns, health care resource use and associated costs in these patients. METHODS: This cohort study using the US claims database PharMetrics included adults with a first prescription of an antidepressant (escitalopram, an SSRI or venlafaxine) associated with a diagnosis of MDD in 2003-2005, and with two diagnoses of anxiety in the year surrounding this first prescription. Treatment patterns, health care resource use and related costs were assessed during the 6-month before and after first prescription, and compared across treatment groups. RESULTS: Of 18,676 patients, 69% were women, and mean age was 40. 25% of patients were prescribed escitalopram, 64% SSRIs, and 11% venlafaxine. Treatment patterns showed a 15% switch rate, a 16% combination rate and 23% of stops with no subsequent relapse (successful treatment stop). Both switch and combination rates were lower with escitalopram vs. SSRIs and venlafaxine (p<0.001 and p=0.002 respectively). Successful treatment stops were more frequent with escitalopram vs. venlafaxine (p<0.001). 6-month total health care costs after treatment initiation were not significantly different than before (US$ 4,656 vs. US$4,254), but the structure of costs differed, with more pharmacy costs (20% vs. 10%), and less inpatient care (36% vs. 51%) after treatment start. Compared with baseline costs, health care costs were decreased with escitalopram and increased with SSRIs and venlafaxine (- US$74 vs. + US$496 and + US$916 respectively). CONCLUSIONS: In patients with MDD and co-morbid anxiety, antidepressant treatment was generally associated with decreased inpatient care. Compared with SSRIs and venlafaxine, escitalopram was associated with less treatment changes and with decreased costs.