In this study, the impact of dosing frequency [once daily with bupropion extended-release (XL) versus twice daily with bupropion sustained-release (SR)] on medication persistence was assessed over a 9-month period in a large cohort of patients with depression in a managed-care setting. Administrative claims data from the Integrated Health Care Information Services National Managed Care Benchmark database were analyzed for patients 18 to 64 years old with a documented diagnosis of depression who began treatment with bupropion XL or SR between September 2003 and February 2004. Persistence of use was higher with once-daily bupropion XL (n = 1074) than with twice-daily bupropion SR (n = 1917) across measures assessed by univariate tests of proportions. The mean (+/-SD) number of days between the first and last prescription claims was longer with bupropion XL (128.37 +/- 103.46 days) than with bupropion SR (82.31 +/- 96.86 days) (P < 0.0001). The bupropion XL cohort had higher persistency of use than the bupropion SR cohort (mean +/- SD = 0.47 +/- 0.38 versus 0.30 +/- 0.36) (P < 0.0001) and a higher medication possession ratio (mean +/- SD = 0.50 +/- 0.33 versus 0.36 +/- 0.31) (P < 0.0001). Medication persistency >0.7 and a medication possession ratio >0.7 were almost twice as likely in the bupropion XL cohort (38.5% and 32.0%, respectively) than in the bupropion SR cohort (21.5% and 17.0%, respectively). Results of multivariate analyses adjusted for age, gender, and index date support the univariate analyses. Because better persistence and adherence may be associated with less likelihood of relapse and lower depression-associated health care utilization and economic burden, health care providers should consider the potential benefits of initiating treatment with bupropion XL for bupropion candidates and for switching bupropion SR recipients to treatment with bupropion XL.