This study aims to validate radioactive seed localization (RSL) as an alternative to wire localization (WL) in the operative excision of nonpalpable breast lesions. Eligible patients were recruited sequentially. A sample of 99 patients treated with WL was compared to the next 383 patients treated with RSL. Margins were considered "negative" if > or =2 mm from in-situ and invasive disease. Pain and convenience scores were recorded on a 10-point scale. Patient characteristics and histology were similar. The lesion and localization device were retrieved in all patients. Margins of the first specimen were negative in 73% of RSL patients, versus 54% of WL patients (p < 0.001). A second operation was required in 8% of RSL patients to achieve negative margins, versus 25% of WL patients (p < 0.001). Pain scores were not statistically different. However, the RSL group had higher convenience scores (p = 0.015). RSL is safe, effective, and compared to WL, reduces the rates of intraoperative re-excision and reoperation for positive margins by 68%. Patient satisfaction is improved with RSL. We strongly favor RSL over WL.