IntroductionResearch into the transplantation of solid organs from animals (xenotransplantation) is generating interest and curiosity given that this could be a way of resolving the shortage in transplant organs. However, the fact is that currently xenotransplantation is far from becoming a clinical practice.ObjectiveTo analyse the attitude of medical students from Spanish universities towards the donation of organs from animals and to determine the factors affecting their attitudes.Material and MethodsType of study: A sociological, interdisciplinary, observational and multicentre study in Spain. Study population: Students enrolled on the medical degree in Spain (n = 34 000). Sample size: A sample of 9598 students (a confidence level of 99% and precision of 1%) stratified by geographical area and academic year. Instrument of measurement: A validated questionnaire of attitude towards organ xenotransplantation (PCID-XenoTx RIOS) which was self-administered and completed anonymously.ResultsA completion rate of 95.7% (n = 9275) was obtained. If the results of xenotransplantation were as good as in human donation, 81% (n = 7491) would be in favour, 3% (n = 308) against and 16% (n = 1476) undecided. The following variables affected this attitude: sex (P < 0.001); academic year (P < 0.001); discussion of transplantation with one's family (P < 0.001) and friends (P < 0.001); the opinion of one's partner (P < 0.001); the respondent's attitude towards organ donation (P < 0.001); religion (P < 0.001); and participation in altruistic activities (P < 0.001). The following variables persisted in the multivariate analysis: (1) being a female (OR = 1.794; P < 0.001); (2) academic year (OR = 2.487; P < 0.001); (3) having spoken about the issue with one's family (OR = 1.200; P = 0.019); (4) the favourable opinion of one's partner (OR = 1.526; P = 0.028); (5) an attitude in favour of donation (OR = 2.087; P < 0.001); (6) being an atheist/agnostic, (OR = 2.5; P < 0.001); and (7) a belief that one's religion is in favour of transplantation (OR = 1.317; P = 0.005).ConclusionsSpanish medical students have a favourable attitude towards xenotransplantation. This willingness and interest could be a decisive platform for the development and strengthening of research, both for centres with a pre-clinical xenotransplantation programme and new healthcare centres.