To analyze the level of understanding of the brain death concept among medical students in universities in Spain. This cross-sectional sociological, interdisciplinary, and multicenter study was performed on 9598 medical students in Spain. The sample was stratified by geographical area and academic year. A previously validated self-reported measure of brain death knowledge (questionnaire Proyecto Colaborativo Internacional Donante sobre la Donación y Transplante de Organos) was completed anonymously by students. Respondents completed 9275 surveys for a completion rate of 95.7%. Of those, 67% (n = 6190) of the respondents understood the brain death concept. Of the rest, 28% (n = 2652) did not know what it meant, and the remaining 5% (n = 433) believed that it did not mean that the patient was dead. The variables related to a correct understanding of the concept were: (1) being older (P < .001), (2) studying at a public university (P < .001), (3) year of medical school (P < .001), (4) studying at one of the universities in the south of Spain (P = .003), (5) having discussed donation and transplantation with the family (P < .001), (6) having spoken to friends about the matter (P < .001), (7) a partner’s favorable attitude toward donation and transplantation (P < .001), and (8) religious beliefs (P < .001). Sixty-seven percent of medical students know the concept of brain death, and knowledge improved as they advanced in their degree.