Sentinel node biopsy has become the standard method for lymphatic staging in early-stage breast cancer and melanomas. The most commonly used technique uses both a radioactive tracer as well as blue dye, usually isosulfan blue. In this report, we discuss two episodes of anaphylaxis to isosulfan blue during lymphatic mapping, occurring 12 years and 3339 lymphatic mapping cases after adoption of the technique, and discuss management issues raised by these events.