The residency program in Emergency Medicine should include formal training in Non-Technical Skills (NTS). We evaluated the effectiveness of a program based on High-Fidelity Simulation (HFS) to improve the leadership and communication skills of residents in Emergency Medicine. In this prospective observational study, we performed 6 simulation sessions, each with 3 scenarios about the management of the critically ill. In the second to the fifth session, participants received specific training about: the ABCDE (Airway, Breathing, Circulation, Disability, Exposure) approach, leadership, communication, and situation awareness, one topic per session. Technical Skills (TS) were measured as the percentage of critical actions correctly performed by participants during the primary examination. NTS were rated by the Leadership Behavior Description Questionnaire (LBDQ), Communication Competence Questionnaire (CCP), and Clinical Teamwork Scale (CTS). The trend over the following sessions was evaluated. We examined 90 scenarios, 15 scenarios per session (three scenarios repeated 5 times). The LBDQ score reached in the fifth and sixth sessions (fifth: 25 [20-30]; sixth: 25 [22-29]), was significantly higher than that obtained in the first, second, and third ones (first: 23 [18-24]; second: 22 [16-26]; third: 20 [14-26], all p<0.05). The percentage of correctly performed actions during ABCDE assessment (10 [7-14] vs. 17 [15-19]), as well as CCQ scores (46 [42-48] vs. 51 [47-52]) and CTS scores (82 [64-88] vs. 94 [91-101], all p<0.01), increased significantly between the first and the last session. HFS confirmed to be an effective instrument to allow Emergency Medicine residents to acquire NTS skills in a safe environment.