BACKGROUND Up to 10% of the population reports an "allergy" to penicillin, whereas approximately 1.1% has positive penicillin skin test results. Where penicillin skin tests are unavailable, some have advocated using history to decide whether to use a penicillin-related antibiotic. OBJECTIVE To determine if clinical history predicts penicillin skin test results. METHODS Retrospective medical record review of 94 consecutive patients who had previously taken penicillin referred for penicillin allergy. Case histories were taken, penicillin skin tests performed, and an oral challenge recommended if skin test results were negative. RESULTS Of 91 cases studied, the average patient age was 27 years (range, 6 months to 82 years; 36% female). Fifty-two (57%) experienced hives as their main adverse reaction. Sixteen (18%) had at least 1 positive test result. Of this group, 9 had hives as their main symptom, whereas 1 had respiratory problems and 1 had angioedema. Most patients with positive skin test results had experienced their reaction at least 3 years ago. Regression analysis showed that age, sex, and clinical history, including type of reaction, time of reaction after penicillin ingestion, or time since the last reaction, were not associated with skin test positivity. Seventy-two (96%) of the 75 patients who had negative skin test results underwent oral challenge. Seventy had negative challenge results. The negative predictive value of a negative penicillin skin test result was 97%. CONCLUSIONS Clinical history was not predictive of subsequent penicillin skin test results.