The majority of patients with nonpalpable breast lesions are eligible for breast conserving surgery guided by some kind of lesion localization. The current standard is wire-guided localization (WGL) even though it has several disadvantages, the most important one being the considerable proportion of patients with insufficient resection margin. These patients require a reoperation. New methods in the field of radioguided surgery (RGS) have been developed including radioguided occult lesion localization (ROLL) and radioactive seed localization (RSL). Especially RSL is a very promising technique. Guided by ultrasound a small titanium seed containing typically 1-10 MBq of radioactive iodine-125 is placed in the centre of the nonpalpable breast lesion. During the operation the seed is located with a hand-held gamma probe. To date, only few cohort studies exist on the feasibility of RSL, and the method has only been tested in one randomized trial. The results are either equal to or superior to those obtained with WGL, with regards to achieving free margins and low reoperation rates. Additionally, the RSL technique is less unpleasant for the patient and more flexible regarding preoperative logistics. The seed can be placed a few days before surgery, in contrast to the wire used in WGL, which has to be placed within few hours of surgery. RSL has quickly become popular in surgical and radiological teams that have used the technique and will probably become an important tool for preoperative localization of nonpalpable breast lesions in the near future.