PIP: Endogamous Muslim groups in Delhi and Lucknow, India, were studied to discover the effects of consanguineous marriage on fertility, mortality, and net-fertility rates. Sayyad Shias have a much higher frequency of parental consanguinity. Consanguineous marriages occurred among the following groups in descending order of frequency: Sheikh, Pathan, and Moghul Sumnis. Different forms of inbreeding occurred among the various groups. Most Muslims oppose family planning on religous grounds. In both Sayyad Shias and Sheikh Sumni consanguineous marriages there was a higher fertility rate than among non-consanguineous marriages. The net-fertility rate was not higher, because mortality before 21 was highest among first cousins.