Association of penicillin allergy with idiopathic anaphylaxis.

Idiopathic urticaria is a common and usually self-limited illness that is occasionally associated with life-threatening idiopathic anaphylaxis. A case is presented in which urticaria existed for 30 years before tests that revealed penicillin allergy as the probable cause. Our findings suggest that evaluation for penicillin allergy may be useful in some cases of urticaria.