Accelerated partial breast irradiation (APBI) using the implanted brachytherapy device MammoSite® was approved for routine use by the Food and Drug Administration in 2002. The American Society of Breast Surgeons MammoSite® Breast Brachytherapy Registry served as a guideline for our institution to begin offering this treatment in 2005. This report reviews our available data to provide an analysis of patient outcomes over 12 years of use at a single institution. A retrospective review was conducted of records of 150 patients who underwent APBI or attempted APBI after breast-sparing surgeries between 2006 and 2017. These charts were analyzed for documentation of patient age, cancer stage, incidence of recurrence, and posttreatment complications. Of the patients evaluated, 99 per cent (149/150) completed treatment. The median time since treatment completion is now 8.9 years. One hundred eleven patients (74% ) are now greater than five years posttreatment. Ipsilateral breast recurrence was found in 2.7 per cent of patients (4/149), and 1.3 per cent of patients (2/149) developed new primary breast tumors. Acute complications, mostly skin erythema (21%), were uncommon and self-limited. Subacute effects were generally fibrosis (13%) and mild local pain (9.4%). APBI for breast cancer after breast-conserving surgery continues to be used at our institution for select patients with good outcomes. Local control and toxicity are similar to that reported in the literature. Five-year local recurrence rates compare favorably with national trials. Occasional complications included fibrosis, persistent pain, and skin irritation.