The aim of this study was to develop and evaluate a triage method to prevent unnecessary emergency department visits of out-of-hospital poisoned patients. From October 2003 to September 2004, the calls that lay persons gave to the Seoul Emergency Medical Information Center to seek advice on the out-of-hospital poisoned patients were enrolled. We designed a triage protocol that consisted of five factors and applied it to the patients. According to the medical outcomes, we classified the patients into two groups, the toxicity-positive and the toxicity-negative. We arranged the factors on the basis of the priority that was determined in order of the odds ratio of each factor for the toxicity-positive and made a flow chart as a triage method. Then we calculated a sensitivity, specificity, positive predictive value and negative predictive value of the method. We regarded the specificity as the ability of the method and the sensitivity as the safety. A total of 220 patients were enrolled in this study. The method showed a sensitivity, specificity, positive predictive value, and negative predictive value of 99.2%, 53.4%, 76.2%, and 97.9%, respectively. Our triage method prevented 53.4% of the unnecessary emergency department visits of out-of-hospital acutely poisoned patients, safely.