A patient with idiopathic anaphylaxis (IA), classified as generalized IA with frequent episodes, had original episodes in 1985 and has been managed and studied by the authors since 1987. Although her episodes of IA appear to have been controlled by prednisone, progressively larger doses of prednisone have been required. The patient was classified as a patient with corticosteroid-dependent IA, a subset of patients with IA in whom a remission cannot be induced with prednisone and in whom prednisone cannot be stopped. A trial of ketotifen is in progress without definitive effect on prednisone requirement. Because this corticosteroid-dependent patient with IA, which is potentially fatal, cannot be managed on less than 90 mg of alternate-day prednisone, we propose the term malignant IA to categorize such severe cases of IA.