OBJECTIVES: To estimate the impact of different factors in the door-to-doctor time in the emergency department of a private hospital in Southern Brazil using discrete events simulation (DES). METHODS: In a DES model, we estimated the influence of the following factors in door-to-doctor time in the emergency department: (1) triage model (current scenario: same staff for pediatric and adult triage; alternative scenario: separated triage staffs for the adults and pediatric patients); (2) pre-defined goal of number of patients per hour per physician (current scenario: no goal; alternative scenario: minimum of 3 patients per hour per physician as goal); (3) number of physicians (increment of 1 physician – from 3 to 4 – per shift). Patient flow in the emergency department (ED) was assessed before the model development and validated with de ED staff. We assessed patient waiting times through electronic health records and, when necessary, with primary data collection in the ED. Distributions used to depict parameter variability included gamma, lognormal and Erlang. Model development was made using Arena software. RESULTS:  Mean door-to-doctor time was 69 minutes An extra physician per staff resulted in a mean 17.8 minutes reduction of door-to-doctor time, while a goal of at least 3 patients per hour decreased the mean time by 12.7 minutes. The separated triage had an estimated impact of 4.3 minutes reduction. The predicted decrease in time with the combination of the three aforementioned factors was 23.4 minutes. CONCLUSIONS: DES can be used to forecast the impact of structural, staff and processes changes in healthcare facilities. The information provided may help the process of decision making for healthcare managers.