OBJECTIVES: To assess the impact of comorbid depression and pain on treatment costs for individuals diagnosed with Generalized Anxiety Disorder (GAD). METHODS: Using the PharMetrics Integrated Outcomes Database, individuals were included in the study if they were: diagnosed with GAD (ICD9-CM: 30002) between 1/2003 and 6/2004 (the diagnosis date as the index date); no diagnosis of GAD 6-month prior the index date; continuously eligible for insurance coverage for 6-month prior and 12-month post the index date; and 18-64 years old. Total and component treatment costs during the year following GAD diagnosis were compared among four patient groups: GAD only; GAD/depression; GAD/pain; and GAD/depression/pain. General Linear Models (GLM) controlling patient demographics (age, gender, region and type of insurance plan), clinical characteristics (provider specialty and other comorbidities), and prior costs were used to evaluate the marginal impact of comorbid depression and/or pain on treatment costs. RESULTS: Of 36,435 patients (mean age 41.5 years; 67% female) included in this study, 23.8% were GAD only, 15.5% GAD/depression, 32.8% GAD/pain, and 28.0% GAD/depression/pain. The average total annual treatment costs were $8377 for all patients. Results from GLM regressions showed that compared to patients with GAD only, total treatment costs were $837 higher for GAD patients with depression (p<.001), $3429 higher for GAD patients with pain (p<.001), and $7503 higher for those with both depression and pain (p<.001). Similar results were also found for component costs including inpatient and outpatient costs. CONCLUSION: This study demonstrated that the majority of GAD patients also suffered from depression or pain and a large portion had both depression and pain. Comorbid depression and pain had significant impact on treatment costs, especially those with pain or with both depression and pain. This suggested that an optimal treatment strategy of GAD needs to take comorbid depression and pain into consideration.