Background: Research on the attitudes of Saudi adults towards consanguinity is scarce. The study aimed to explore the attitudes towards consanguinity and its associations with socio-demographic characteristics in a sample of Saudi adults. Methods: A cross-sectional study was conducted using a self-administered questionnaire. A total of 386 outpatient waiting-area attendees at King Abdul-Aziz Medical City-Riyadh were included. Participants were asked about their socio-demographic characteristics, attitude towards consanguinity and the reasons behind this. Results: The positive attitude towards consanguinity among the study respondents was 48.1% with 95% confidence interval (42.91–53.33%). Social and traditional culture (59.9%) were found to be the predominant reasons for favoring consanguinity in Saudi Arabia. Evidence against a positive attitude towards consanguinity was noted in respondents who received medical information about consanguinity versus those who had not received medical information (42.3% vs. 57%, p-value = 0.008). According to the multivariate logistic model, the odds of a positive attitude towards consanguinity were 2 times higher for males (adjusted odds ratio [aOR]: 2.2; 95% CI: 1.147, 4.290) and 4.1 times higher in respondents in consanguineous marriages (aOR: 4.1; 95% CI: 2.350, 7.156). The odds of a positive attitude towards consanguinity were 50% less in respondents who received health information on consanguinity compared to those who had not received health information about consanguinity (aOR: 0.50; 95% CI: 0.253, 0.863). Conclusion: One in every two Saudi adults favors consanguinity however, Saudi men and women differ in their attitudes towards consanguinity. Receiving health information on consanguinity was associated with a negative attitude towards this practice.