Pemphigus is an autoimmune blistering skin disease. The clinical manifestations of the most common variant, pemphigus vulgaris, are caused by pathogenic antibodies directed against desmogleins 1 and 3. A number of medications have been reported to induce pemphigus variants. Penicillamine is the most common, although other medications, including penicillin, have been rarely implicated. In this analysis of drug purchases from a health maintenance organization central database, Heymann et al demonstrate that penicillin may be associated with the development of pemphigus, although a causal link was not clearly established.