Objective The conduct of a medical interview is a challenging skill, even for the most qualified physicians. Since a training is needed to acquire the necessary skills to conduct an interview with a patient, we compared role-play with standardized patients (SP) training and a conventional lecture for the acquisition of communications skills in undergraduate medical students. Methods An entire promotion of third year undergraduate medical students, who never received any lessons about communications skills, were randomized into 4 arms: 1) SP 2 months before the testing of medical communications skills (SP); 2) conventional lecture 2 months before the testing (CL); 3) two control groups (CG) without any intervention, tested either at the beginning of the study or two months later. Students were blindly assessed by trained physicians with a modified 17-items Calgary-Cambridge scale. Results 388 students (98.7%) participated. SP performed better than CL, with significant statistical differences regarding 5 skills: the use of open and closed questions, encouraging patient responses, inviting the patient to clarify the missing items, encouraging of the patient’s emotions, and managing the time and the conduct of the interview. The SP group specifically improved communications skills between the SP training and testing sessions regarding 2 skills: the use of open and closed questions and encouraging patient responses. No improvements in communications skills were observed in CG between the two time points, ruling out a possible time effect. Conclusion Role-play with standardized patients appears more efficient than conventional lecture to acquire communication skills in undergraduate medical students.