Introduction Research 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. Objective To 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 Methods Type 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. Results A 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). Conclusions Spanish 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.