OBJECTIVE: To evaluate the likelihood of alpha-adrenergic antagonist (alpha-blocker) discontinuation in combination with dutasteride or finasteride among patients aged > or =65 years with enlarged prostate. METHOD: This retrospective analysis used 2003-2006 data representing more than 30 million managed care members. Medical/pharmacy claims were used to select patients, matched 1:1 using propensity scoring. The proportion remaining on alpha-blocker therapy more than 12 months and time to discontinuation were compared between groups, controlling for covariates using survival analysis. RESULTS: The matched sample included 1674 patients. Alpha-blocker therapy discontinuation was observed at 90 days (86.9% dutasteride patients and 91.8% finasteride patients remained on alpha-blocker therapy). After 12 months, more dutasteride patients discontinued (38.1% remained) alpha-blocker therapy than finasteride patients (56.3% remained). CONCLUSIONS: Patients discontinued alpha-blocker therapy as early as 3 months. Those taking dutasteride were 64% more likely to discontinue alpha-blocker therapy than patients taking finasteride. Dutasteride's impact on discontinuation may have important implications and should be examined further.