Telephone nurse triage services are becoming increasingly common in healthcare systems worldwide. Florianópolis (Santa Catarina State, Brazil) is the first municipality in the country to provide this service in its public health system. This study adopted a quantitative, descriptive, and analytical methodology to evaluate the impact of this program on overall costs of the public health system. The research examined all 33,869 calls received by the telephone triage service from March 16 to October 31 in 2020, and calculated the program costs during the period. Avoided cost were calculated by the difference between estimated consultation costs considering patient-stated first alternative and the program recommendation after triage. Analyzing only the costs for the municipality of Florianópolis, the program's costs exceeded avoided costs by almost BRL 2.5 million during the period. By expanding the analysis to include costs of emergency department consultation - not administered by the municipality - based on data from previous research, we found that the program spares BRL 34.59 per call, a 21% cost reduction for the health system. Considering the preliminary results of the study and its limitations, it is understood that the service of telephone nurse triage can reduce costs in the healthcare system.