Pregnancy-associated breast cancer is rare, but this clinical situation arises in 1/10,000–1/3000 pregnancies. In patients presenting an early-stage breast tumor devoid of clinically pathological lymph node, sentinel lymph node (SLN) biopsy has not yet been validated as a routine procedure for pregnant women due to the lack of data in the literature. The blue dye injection is not recommended because of 2% theoretical risk of anaphylactic shock. Several studies have shown that Tc^99m injection at conventional dose between 12.1 and 18.5MBq exposed the fetus to an irradiation between 0.011 and 0.0245mSv much below the 50mSv recommended threshold. As evidenced by lymphoscintigraphy scans, the dose of injected Tc^99m is localized at the injection site and in the SLN. According to the literature, the SLN technique does not seem to impact the fetal or obstetrical prognosis. Studies involving larger cohorts are required to confirm these data and to indicate this technique in pregnant women. Considering the benefit for the patient and the low risk incurred on both fetal and obstetrical levels, it appears reasonable to discuss the indication of SLN on a case-by-case basis in multidisciplinary oncologic meetings.