Isosulfan blue is a commonly used agent in the detection of sentinel lymph nodes during cancer surgery. Similar to any drug, it is possible to have an allergic reaction to this increasingly popular chemical during breast cancer operations. We present one case of anaphylactic shock in response to injection of isosulfan blue for the purpose of localizing the sentinel node and review the medical literature. A thorough knowledge of possible isosulfan blue side effects, including their presentation and subsequent therapy, is essential for the modern breast surgeon.