Although a high proportion of marriages in Asia are consanguineous (i.e. contracted between close biological relatives), with some notable exceptions, there is a death of demographic and anthropological literature on the association between consanguinity and fertility. This paper presents an overview of the prevalence of consanguineous marriages in selected South and Southeast Asian countries, followed by an assessment of the association between consanguinity and fertility. The association between consanguinity and fertility was assessed reviewing published literature and analyzing demographic and health survey (DHS) data from Pakistan and India. Results of the review of published literature showed higher fertility among women in the first-cousin unions compared to those married to non-relatives. In the DHS analyses, consanguinity was found to be associated with a number of direct and indirect determinants of fertility, including lower maternal education, lower maternal age at marriage, lower contraceptive use, and rural residence. At the multivariate level, adjusted mean fertility was found to be lower among women in the first-cousin unions in the Pakistani DHS data, while for the Indian DHS, adjusted mean fertility levels were similar in the first-cousin and non-consanguineous marriages. The pathways through which consanguinity affects fertility in Asian populations are evaluated and discussed.