OBJECTIVE: The prescription of prostate non-selective alpha-1 antagonists (terazosin, doxazosin, prazosin) may require extra health care visits for dose titration and for monitoring treatment safety and effectiveness. From a retrospective cohort study using pension related fee-for-service supplementary Medigap health claims data, we estimated the impact of alpha-1 antagonist initiation on healthcare use and costs for men with BPH. METHODS: Claims data from a two year period included medical and prescription drug information for 53,824 men with BPH. We compared men who initiated alpha-1 antagonists with a random sample of nonusers. Inpatient and outpatient costs were calculated as the sum of the Medicare paid amount, the Medigap co-pay amount, and the Medigap deductible amount. Comparisons used generalized estimating equation (GEE) or Poisson regression methods to estimate the change from four months pre- to four months post-initiation and an imputed date for non-users. This period coincided with the recommended time for treatment titration and a period of increased hypotensive event risk in this population. RESULTS: Adjusting for baseline healthcare use, age, and co-morbidity, alpha-1 antagonist initiators had a mean of 4.2 more physician visits post-initiation than men who did not initiate among those who did not use other antihypertensives and 5.8 more visits among men who did use antihypertensives (p<0.05). The corresponding adjusted difference in cost of physician visits was $176 per man for those who did not use other antihypertensives and $267 for those who did use other antihypertensives (p<0.05). Initiation was also significantly associated with an increase of 0.15 hospital stays per 1,000 person-days among non-users of other antihypertensives and an increase of 0.24 hospital stays per 1,000 person-days among users of other antihypertensives. CONCLUSION: The increased number of physician visits, hospital stays, and physician visit costs post-initiation should be considered in cost-effectiveness analyses of BPH treatments.