A textbook hypothesis about divorce is that heterogamous marriages are more likely to end in divorce than homogamous marriages. We analyse vital statistics on the population of the Netherlands, which provide a unique and powerful opportunity to test this hypothesis. All marriages formed between 1974 and 1984 (nearly 1 million marriages) are traced in the divorce records and multivariate logistic regression models are used to analyse the effects on divorce of heterogamy in religion and national origin. Our analyses confirm the hypothesis for marriages that cross the Protestant-Catholic or the Jewish-Gentile boundary. Heterogamy effects are weaker for marriages involving Protestants or unaffiliated persons. Marriages between Dutch and other nationalities have a higher risk of divorce, the more so the greater the cultural differences between the two groups. Overall, the evidence supports the view that, in the Netherlands, new group boundaries are more difficult to cross than old group boundaries.