PURPOSE: Selective transarterial embolization for renal angiomyolipomas is effective in preventing or limiting hemorrhage and preserving normal parenchyma. Data are insufficient regarding the safety and efficacy of embolic agents. We compared transarterial embolization of angiomyolipomas using embolic agents of different sizes. MATERIALS AND METHODS: We performed a retrospective review of all transarterial angiomyolipoma embolizations from 1999 to 2010, and evaluated demographics, procedural data, embolization response and outcomes comparing smaller (less than 150 microns) and larger (more than 150 microns) embolic agents. RESULTS: Overall 48 patients underwent 66 embolization procedures for 72 angiomyolipomas. Smaller agents were used more commonly (58%). Age, gender, indications, pre-embolization angiomyolipoma size and prevalence of tuberous sclerosis were similar between the groups. Angiomyolipomas decreased a mean±SD 25%±18% after embolization with no differences between the groups (p=0.24). There were 10 angiomyolipomas that required 14 repeat embolizations (median 14 months). Repeat embolization of the same mass was almost sixfold more likely in those embolized with smaller agents (OR 5.88, 95% CI 1.64-20.8, p=0.002). Complications were similar between the groups, although 2 of 3 patients with acute respiratory distress underwent embolization with smaller agents. Patients with tuberous sclerosis had similar angiomyolipoma size, decrease in angiomyolipoma size, followup, complications and need for repeat embolization. Practice patterns changed regarding embolization agent size during the study period. CONCLUSIONS: Angioembolization with larger embolic agents is associated with higher long-term efficacy compared to smaller agents. Due to concerns for serious pulmonary complications, we no longer use agents smaller than 150 microns. Prospective studies are necessary to evaluate the optimal embolization technique to achieve durable outcomes without increasing patient morbidity.