[en] Immigration and mobility in the medieval and post-medieval periods in Norway have, up until now, mainly been discussed on the basis of historical sources. This paper presents the results of stable oxygen isotope (δ18O) analyses of the 1st and 3rd molars from 95 individuals from medieval and post-medieval Trondheim, as well as new information about the δ18O composition in the precipitation and drinking water in Trondheim. Through these analyses, the authors have attempted to shed light on the age of migrating individuals and directions of migration, to investigate temporal changes with regard to migration, and to make suggestions regarding the proportion of immigrants to locals in the population.The results show that the majority of the immigrants came from areas to the north or east of Trondheim, and some travelled at least 800–1000 km to come to Trondheim. It has also been shown that a large proportion of the medieval individuals moved during childhood. Both with regard to child mobility and migration in general, the evidence suggests that the migratory activity decreased from the medieval to the post-medieval period.