To analyze the ability of medical students to be integrated in the teaching of basic abdominal ultrasound using a peer-mentoring design. Thirty medical students previously trained in basic abdominal ultrasound (mentors) had to teach all fourth-year students (n = 136) from a single academic year the same training they had received. There were 3 stages to the ultrasound teaching: theoretical (online course); basic training (3 practical sessions in which students were guaranteed to have had a minimum of 15 hours of practical experience with ultrasound and performed at least 20 basic abdominal ultrasound studies); and evaluation (objective structured clinical examination in which students had to obtain the basic abdominal views and to identify 17 structures). The mean grade ± SD obtained was 8.71 ± 1.53 of a possible 10 points. Only 2 students (1.56%) obtained a grade lower than 5, and 14 students (10.86%) obtained a grade lower than 7. A total of 33 students (25.5%) achieved the maximum grade. The structures most easily identified were the liver, the right kidney, and the urinary bladder, with 97.7% of correct answers. Students obtained the poorest results when trying to identify the left and right cardiac cavities (subxiphoid view), with only 53.5% and 55.8% of correct answers, respectively. Teaching based on peer mentoring achieved an adequate level of training in basic abdominal ultrasound. The students acquired these skills in a relatively short training period. These results suggest that peer mentoring can facilitate the large-scale implementation of ultrasound teaching in undergraduate students.