Data on the shape of teeth can be used to test hypotheses about the relationship between adaptive and stochastic processes involved in morphologic divergence between populations. We used 7 two-dimensional landmarks to quantify shape in the upper 1st molar of the arctic fox (Vulpes lagopus, formerly Alopex lagopus) and tested for differences in molar shape between populations. The arctic fox is widely distributed throughout the Holarctic region, is found on several Bering Sea islands, and occurs in a range of habitats. This broad geographic and ecological distribution allowed for simultaneous testing of the relationship between molar shape and several factors including environmental parameters, geographic distances, and time since population divergence. We identified 11 populations for comparison, located from Siberia to Greenland, including 4 Bering Sea island populations. We found that shape differed only slightly among mainland populations, whereas island populations differed significantly from each other and from all mainland populations. Divergence in tooth shape was significantly correlated with geographic distance. Because differences in annual temperature and annual rainfall often underlie differences in local environmental conditions, we used these variables to test for differences in tooth shape resulting from local adaptation. Shape did not correlate significantly with either mean annual temperature or precipitation. Observed divergences in tooth shape between populations may be explained by local adaptation, allometry related to between-population size differences, and stochastic processes. The results are most consistent with a combination of allometry and stochastic processes, but local adaptation cannot be excluded.