We noticed a seemingly high prevalence of penicillin allergy in patients who had been diagnosed with peritonsillar abscess (PTA) at our institution. To formally investigate this observation, we reviewed the emergency room (ER) records of 118 patients who had presented between Jan. 1, 1995, and Dec. 31, 1999, with suspected PTA. A diagnosis of PTA was confirmed by the presence of pus on incision and drainage in 78 of these patients (66.1%). The remaining 40 patients (33.9%) were diagnosed with peritonsillar cellulitis (PTC). Of the 78 patients with confirmed PTA, 13 (16.7%) self-reported an allergy to an antibiotic, including 11 (14.1%) who claimed to be allergic to penicillin. In the 40 patients with PTC, the corresponding figures were only 3 (7.5%) and 1 (2.5%). The difference between the PTA and PTC groups with respect to the prevalence of self-reported penicillin allergy was statistically significant (p < 0.05). We also compared the prevalence of antibiotic allergies in our patients with that of 1,893 consecutively presenting patients whose records had been entered into a pharmacy database at our institution. We found that the overall prevalence of patient-reported penicillin allergy in our PTA group was similar to that of the database population, although penicillin allergy did account for a greater percentage of all antibiotic allergies (84.6%) in our PTA group than in the larger population (62.8%). In our series, patients with PTA were more likely to have reported an allergy to penicillin than were patients without an abscess. Additionally, the prevalence of patient-reported antibiotic allergy is high at our institution. Although self-reported penicillin allergy may not represent a true hypersensitivity reaction, it can influence antibiotic selection and/or compliance. Prospective studies are needed to determine what influence allergic status and antibiotic choice has on abscess development.