Background: Triage is a mainstay of early mass casualty incident (MCI) management. Standardized triage protocols aim at providing valid and reproducible results and, thus, improve triage quality. To date, there is little data supporting the extent and content of training and re-training on using such triage protocols within the Emergency Medical Services (EMS). The study objective was to assess the decline in triage skills indicating a minimum time interval for re-training. In addition, the effect of a one-hour repeating lesson on triage quality was analyzed. Methods: A dummy based trial on primary MCI triage with yearly follow-up after initial training using the ASAV algorithm (Amberg-Schwandorf Algorithm for Primary Triage) was undertaken. Triage was assessed concerning accuracy, sensitivity, specificity, over-triage, under-triage, time requirement, and a comprehensive performance measure. A subgroup analysis of professional paramedics was made. Results: Nine hundred ninety triage procedures performed by 51 providers were analyzed. At 1 year after initial training, triage accuracy and overall performance dropped significantly. Professional paramedic's rate of correctly assigned triage categories deteriorated from 84 to 71%, and the overall performance score decreased from 95 to 90 points (maximum = 100). The observed decline in triage performance at 1 year after education made it necessary to conduct retraining. A brief didactic lecture of 45 min duration increased accuracy to 88% and the overall performance measure to 97. Conclusions: To improve disaster preparedness, triage skills should be refreshed yearly by a brief re-education of all EMS providers.