Background: Assimilation models of infant outcomes among immigrants have received considerable attention in the social sciences. However, little effort has been made to investigate how these models are influenced by the source country.

Objective: We investigate the relationship between infant mortality and the number of years since maternal migration and whether or not this relationship varies with maternal source country.

Methods: We use an extensive dataset which includes all of the births in Norway between 1992-2010, augmented by information on the source country and other maternal characteristics. By measuring the source country infant mortality rate at the time the mother came to Norway, we are able to account for circumstances in the country the mother left behind. We apply assimilation models which allow for interactions between source country characteristics and maternal years since migration. We also fit models in which age at maternal migration replaces maternal years since migration.

Results: Our analyses generated three main findings. First, an assimilation process has taken place, as the infant mortality rate declined with the number of years since maternal migration. Second, maternal source country characteristics are significantly associated with infant mortality rates in Norway. Mothers from countries with high infant mortality rates (e.g., countries in Africa and Asia) had higher infant mortality rates than mothers from countries with low infant mortality rates (e.g., countries in Europe). Third, the assimilation process varied by maternal source country: i.e., the assimilation process was more pronounced among mothers from countries with high infant mortality rates than among those from countries with low infant mortality rates.

Conclusions: The source country is an important predictor of the assimilation profiles. This study contributes to the existing literature on assimilation by emphasising the significance of the source country.