This Viewpoint compares MammoSite® brachytherapy with other forms of partial breast irradiation. Although very few reports on clinical efficacy have been published, indications so far are that the MammoSite®catheter is technically simple, adequately spares normal tissues, and is associated with a favorable cosmetic outcome and toxicity profile. The choice of the optimal irradiation method remains complex and requires input from both treating physicians and their patients.