Very few cases of hypersensitivity due to ingestion of mustard have been described in the literature, although this spice enjoys widespread use. We present three cases of anaphylactic reactions to ingestion of a small amount of mustard sauce. In our patients we performed skin prick tests with mustard and with the rest of the vegetables belonging to the Cruciferae family. We also performed skin prick tests with common pneumoallergens. We measured specific serum IgE to mustard using the CAP System (Pharmacia). Oral challenges with the other vegetables of the Cruciferae family were performed in the patients with no evidence of previous tolerance. Skin prick tests and specific serum IgE determinations to mustard were positive in all three patients. The tests with the rest of the vegetables belonging to the same family were negative. In conclusion, we consider that skin prick tests and the measurement of specific serum IgE to mustard are good methods for the diagnosis of mustard hypersensitivity. We did not detect cross-sensitivity with other vegetables of the same family or with pneumoallergens.