Objective: This study examined the health service utilization and treatment costs among depression patients who received antidepressant medication, psychotherapy or both. Methods: This study used medical and pharmacy claims data from 220,620 employees from three employer groups from September 2002 to December 2003. Depression patients (n=4653) were identified using ICD-9 diagnosis codes from medical claims data. Differences in treatment costs and comorbid conditions were examined between depression patients who received psychotherapy and those who did not. Results: Among eligible members, 4,653 (2.1%) had a primary diagnosis of depression. Nearly 70% were female with an average age of 39.7 years. Approximately half of the depression patients (46.9%) received antidepressant medication alone while 34.2% of patients received both psychotherapy and medication. Only 19.3% of depression patients received psychotherapy without medications. The average total treatment cost for depression patients who received both psychotherapy and medications was $10,565, while the average treatment cost for patients who only used medication was $10,014. These treatment costs were not significantly different. The average treatment cost for psychotherapy alone was $3,945. The most frequent comorbid conditions among depression patients were musculoskeletal and chronic pain (29.9%), anxiety (26.6%), injuries (18.7%), hypertension (14.4%), asthma (6.5%), diabetes (6.1%), arthritis (5.4%), urinary tract infection (4.4%) and drug dependence and alcohol abuse (4.1%). Depression patients who received both medication and psychotherapy had significantly more comorbid anxiety (33.1%) and drug and alcohol abuse (5.8%) than those who received medications or psychotherapy alone (p<0.001). Conclusion: Depression patients who used psychotherapy including antidepressant medications did not have significantly different health care costs than depression patients who did not receive psychotherapy treatments. Depression patients with comorbid psychological conditions such as anxiety or drug abuse were more likely to receive psychotherapy treatment (p<0.001).