In the years since the introduction of this procedure, we have made great strides in gathering data regarding the clinical outcome of this procedure and, just as important, in understanding some mechanisms for the clinical improvements we see. Additional study is needed of the embolic material and the comparative effectiveness of the available materials. Ideally, this should be within the context of a randomized study that measures the short- and longer-term clinical outcomes of treatment. We are currently studying PVA and Embospheres in such a study and we would encourage other researchers to explore these outcomes as well. Armed with knowledge based on sound clinical research, we will be able to choose the methods and materials most likely to benefit our patients.