OBJECTIVE: To describe medical negligence and malpractice cases in which a patient with a known penicillin allergy received a β-lactam and experienced an adverse reaction related to the β-lactam. DATA SOURCES: Lexis-Nexus, Westlaw, and Google Scholar were searched. STUDY SELECTIONS: Medical negligence and malpractice cases were eligible for inclusion if they met the following criteria: the plaintiff had a known penicillin allergy, received a β-lactam, and experienced an adverse event. All United States federal and state cases were eligible. RESULTS: Twenty-seven unique cases met the inclusion criteria. Eighteen cases involved the receipt of a penicillin-based antibiotic; of these cases with a known legal outcome, the plaintiff (patient or representative) prevailed or settled in 3 cases and defendants (providers) prevailed in 7 cases. Seven cases involved the receipt of a cephalosporin; of these cases with a known legal outcome, the plaintiff settled with physicians before trial in 1 case and defendants prevailed in 3 cases. Two cases involved the receipt of a carbapenem. Defendants prevailed in one case and the legal outcome of the other case is unknown. In cases in which the defense successfully moved for summary judgment, judges cited a lack of scientific evidence demonstrating a cephalosporin or carbapenem was contraindicated for a patient with a penicillin allergy. CONCLUSION: The cases with published legal outcomes found limited professional liability for clinicians who prescribed cephalosporins or carbapenems to a patient with a known penicillin allergy. These results may decrease the litigation fears of practitioners and risk managers within health care systems.