Patients with a reported penicillin allergy areoften treated with less effective antibiotics. Thisstudy examined the impact of anamnestic penicillinallergy on the length of hospital stay in patientswith erysipelas, a condition for which penicillinis considered the first-line therapy and addressesthe question: Does anamnestic penicillin allergydirectly affect the length of hospital stay in patientswith erysipelas? This retrospective analysis includedpatients who were admitted to the University MedicalCenter Regensburg for the treatment of erysipelas.The data analysed were sex, age at diagnosis,body temperature at admission, C-reactive protein,leucocyte count, procalcitonin, length of hospitalstay, Charlson Comorbidity Index and antibiotictherapy. Patients were divided into 2 groups: withand without the label anamnestic penicillin allergy.Multiple regression analysis showed that patientswith anamnestic penicillin allergy stayed 1.83 dayslonger in hospital than patients without anamnesticpenicillin allergy (mean length of stay 12.17±7.01days for patients with anamnestic penicillin allergycompared to 10.34±4.80 days for patients withoutanamnestic penicillin allergy, as determined by a t-testp=0.046). According to our data, anamnestic penicillinallergy is associated with prolonged hospital stay.Therefore, delabelling of penicillin allergy should bewidely implemented.