If penicillin were the drug of choice for a patient who claims he had an allergic reaction to it 30 years ago, would you consider giving it now?

Such reports are often wrong, due to being overcautious and miscalling some effects in childhood. Although these reports are fraught with inaccuracy, you must consider what's at stake--anaphylaxis. Others feel the margin of safety may be acceptable after so many years without a reaction, but you can never go wrong with the 'abundance of caution' approach.