The marital structure of Italians living in Boston, Massachusetts, in the period 1880–1920 was studied in order to explore the integration process in the urban context. The study analyses endogamy and inbreeding, using data on 15,579 marriages from the parish books of the three Italian parishes of Boston. Endogamic rates are very high and increased in time, ranging from 93·9% to 97·3%. This correlated with the growth of the Italian community and the decline of the biased sex ratio. One parish, Our Lady of Pompeii in the South End, displays lower endogamic rates because of the reduced and scattered population attending it. The rate of consanguineous (2·33%) and isonymous (6·38%) marriages, and the coefficients of inbreeding, alpha; (0·98×10−3) and Ft (0·0159), are similar to those of north Italian populations, and lower than those for south and insular Italy. The parish of Our Lady of Pompeii shows consistently higher values than the other two parishes. Marriages between first and second cousins are the main cause of the above values in each parish. Consanguineous marriages and inbreeding increased over time, from the 1890s, and this is in general agreement, although slightly delayed, with the Italian trend.