BACKGROUND:Neoadjuvant chemotherapy (NAC) is increasingly used in the framework of breast-conserving therapy (BCT). Localization of the initial tumor is essential to guide surgical resection after NAC. This study describes the results obtained with I-125 seed localization in BCT including NAC. PATIENTS AND METHODS:Between January 2009 and December 2010, 85 patients treated with NAC and BCT after I-125 seed localization were included. Radiological and pathological response and resection margins were retrospectively evaluated. RESULTS:BCT was carried out in 85 patients without secondary local excisions. Nineteen patients with unifocal tumors and seven patients with multifocal tumors showed a complete pathological response (P = 0.18). Tumor-free resection margins were obtained in 78 patients (50 patients with unifocal and 28 patients with multifocal tumors, P = 0.27). Focally involved margins were found in four patients (two patients with a unifocal and two patients with a multifocal tumor, P = 0.27). A subsequent mastectomy was carried out in three patients (two patients with multifocal tumors, P = 0.29). CONCLUSIONS:BCT after NAC can be carried out successfully after initial localization with I-125 seeds in both unifocal and multifocal breast tumors with complete resection rates of >90%.