Acute hypersensitivity reactions include different clinical entities, the most threatening of which is anaphylaxis. In the Emergency Department, triage evaluation and decisions can be a determinant of successful treatment. We retrospectively studied 1009 patients who underwent triage in our ED because of acute hypersensitivity over a one year time period. Our aim was to correlate triage priority codes with the clinical manifestations registered at the medical examination, time spent in ED before and after the examination, and admission to hospital or discharge. Emergency codes (red or yellow code) were attributed to 10% of our cases, non-emergency codes (green o white) to 90%. Code grading was changed in 9 patients while awaiting medical evaluation. Severity of symptoms was underestimated in one case, and overestimated in 23. Hospital admission rate was greater among patients with more critical codes. No patient died. In conclusion evaluation, direct observation and re-evaluation are needed for the safe treatment of patients with hypersensitivity reactions in ED, even when initial clinical conditions appear stable