A primary care physician (PCP) not only accompanies the patient in the process of an illness, but throughout his or her life. The confidence we have in these health professionals is fundamental, and their favorable attitude toward organ donation and transplantation (ODT) has a significant influence on the population. Objective: To analyze trust in PCPs among Spanish medical and nursing students, the relationship with their attitude toward ODT, and the factors that condition it. Methods and Design: A sociologic, multicenter, and observational study. Population: medical and nursing students in Spanish universities. Database: Collaborative International Donor Project, stratified by geographic area and academic course. A validated questionnaire (PCID-DTO-RIOS) was self-administered and completed anonymously. A sample of 9598 medical and 10,566 nursing students (99% confidence and precision of ±1%), stratified by geographic area and year of study. Results: Completion rate: 90%. With respect to students’ trust in their physician, 18% (n = 3267) of them totally trust (completely), 45% (n = 8101) trust enough, 30% (n = 5478) of them have not enough trust, and 7% not at all. Comparing groups, medical students totally trust more in PCPs than nursing students (55% vs 45%; P < .000), however, nursing students have less than enough trust in their PCP than medical students (53% vs 47%; P < .000). Students that totally trust in their PCP were more in favor toward ODT than students with not enough trust (83% vs 77%; P < .000). Conclusion: Only 18% of Spanish medical and nursing students totally trust in their PCP. Attitude toward ODT is related to a higher level of trust in PCPs among these students.