CONTEXT: Both benign prostatic hyperplasia (BPH) and cataract formation are common in older men. The alpha-adrenergic receptor blocker tamsulosin is frequently prescribed to treat BPH, and research suggests this drug may increase the intraoperative difficulty of cataract surgery. No studies have documented whether use of tamsulosin or other alpha-blocker drug therapies affect the risk of serious postoperative adverse events. OBJECTIVE: To assess the risk of adverse events following cataract surgery in older men prescribed tamsulosin or other alpha-blocking drugs used to treat BPH. DESIGN, SETTING, AND PATIENTS: Nested case-control analysis of a population-based retrospective cohort study using linked health care databases from Ontario, Canada. We included all men aged 66 years or older who had cataract surgery between 2002 and 2007 (N = 96 128). MAIN OUTCOME MEASURES: A composite of procedures signifying retinal detachment, lost lens or lens fragment, or endophthalmitis occurring within 14 days after cataract surgery. The risk of these adverse events was compared between men treated with tamsulosin or other alpha-blockers and men with no exposure to these medications in the year prior to cataract surgery. We separately examined the association of drug exposure that was either recent (within the 14 days before surgery) or previous (15-365 days before surgery). RESULTS: Overall, 3550 patients (3.7%) in the cohort had recent exposure to tamsulosin and 7426 patients (7.7%) had recent exposure to other alpha-blockers. Two hundred eighty-four patients (0.3%) had an adverse event. We randomly matched 280 of the cases to 1102 controls according to their age, surgeon, and year of surgery. Adverse events were significantly more common among patients with recent tamsulosin exposure (7.5% vs 2.7%; adjusted odds ratio [OR], 2.33; 95% confidence interval [CI], 1.22-4.43) but were not associated with recent exposure to other alpha-blockers (7.5% vs 8.0%; adjusted OR, 0.91; 95% CI, 0.54-1.54) or to previous exposure to either tamsulosin (< or = 1.8% vs 1%; adjusted OR, 0.94; 95% CI, 0.27-3.34) or other alpha-blockers (2.9% vs 2.1%; adjusted OR, 1.08; 95% CI, 0.47-2.48). This corresponds to an estimated number needed to harm (NNH) of 255 (95% CI, 99-1666). CONCLUSIONS: Exposure to tamsulosin within 14 days of cataract surgery was significantly associated with serious postoperative ophthalmic adverse events. There were no significant associations with exposure to other alpha-blocker medications used to treat BPH.