Abstract Study question Which beliefs, motives and psychosocial characteristics distinguish people who are willing to donate their gametes from those who are not? Summary answer Willingness to donate does not differ between men and women, but there are differences in beliefs surrounding its risks, motivations and psychological characteristics. What is known already Previous studies have examined the main psychological characteristics of donors and their motivation to donate. Literature shows that donation is motivated by altruism, with donors being autonomous, self-confident, self-acceptant, and goal-orientated people, guided by meaningful values. Gender differences showed that egg donors often have close contact with infertility situations and motherhood and would like to provide this joy to other women. Sperm donors are more motivated by curiosity about their own fertility and want to spread their “good” genes. However, here is still much to know about what distinguish those who are willing to donate from those who are not. Study design, size, duration This is a cross-sectional study. Data was collected through an online questionnaire, which was disseminated using social media. Inclusion criteria were being adult, within a reproductive age range (between 18 and 35 years old), and fluent in Portuguese. Participants/materials, setting, methods A total of 405 participants completed the survey (305 women and 99 men). The questionnaire included sociodemographic data, beliefs towards gamete donation, reasons that might impact the likelihood of donating, and psychological characteristics through self-administered instruments: Experiences in Close Relationships (ECR), Self-Compassion Scale (SELFCS), Self-Report Altruism Scale (SRAS), NEO Five-Factor Inventory (NEO-FFI). Independent t-test was performed to compare men and women and participants willing or not to donate gametes. Main results and the role of chance Women were 22.86 (±.23) years old and men 24.34 (±.43). A total of 24.2% of participants were willing to donate gametes. There were no gender differences regarding willingness. Significantly more women than men believed that donating gametes might imply psychological risks (p=.001). There were gender differences in motivations to donate. Women were more likely to donate if they could receive fertility counselling (p=.005) and information about infertility (p=.037), and if they could talk with other donors (p<.001) than man. Among women, those willing to donate believed donating would not cause psychological damage (p=.004), would be supported by their social network (p =.006) and would not be criticized by family and friends if they did so (p=.011) compared to those not willing. Psychological differences revealed that women willing to donate presented higher levels of common humanity (p=.003), self-kindness (p=.046), were more altruistic (p<.001) and extroverted (p=.027) than those who were not. No differences were found regarding their attachment orientation. Among men, the only differences distinguishing those who considered donating sperm and those who did not was their altruism levels (p=.047). No differences were found regarding their beliefs towards gamete donation, perceived support regarding the decision, attachment style, self-compassion, and personality traits. Limitations, reasons for caution This study included a convenience sample, and participants lacked adequate information about the legal context and implications of donating gametes in Portugal. The sample size of participants considering donating was small, which may affect our conclusion. Wider implications of the findings Women who consider donating seem to present more salient psychological characteristics than men. Stigma and misinformation might prevent women from considering donating eggs. The possibility of receiving fertility counselling and share their experiences with other donors are valued in the process, which should be considered when recruiting donors. Trial registration number NA