This study uses data on the entire population of the Netherlands to analyze ethnic endogamy among Wrst generation immigrants. First, it replicates patterns observed in earlier studies. Endogamy is higher in immigrant groups that are large, have a favorable sex ratio and that are more segregated spatially. At the individual level endogamy is higher among immigrants who do not speak the host language well, who have lower educational qualiWcations, and who are nonwhite. Second, it extends earlier theoretical work and shows the importance of immigrants’ religious aYliation and the religious diversity of an immigrant group. Third, it examines the severity of some methodological problems of earlier studies on ethnic endogamy