While regional differences in life expectancy have flattened out in Switzerland, we investigate the effect of periurbanization on the geography of mortality. Using data from vital statistics and censuses, we find an increasing intra-urban differentiation of mortality since 1980, especially in the largest and most recently sprawling cities. A non-linear gradient, in which life expectancy is lower in city centres and rural areas than in urban agglomeration belts, has emerged. Age- and cause-specific mortality profiles suggest that lifestyles specific to the population of the city centres and related to the spatial concentration of disadvantaged groups play a dominant role in shaping this pattern. Considering mortality at ages 20-64, a multilevel model applied to census-linked mortality data shows how the mortality advantage observed in periurban areas can be explained by a concentration of highly educated individuals and of families. Excess mortality at ages 20-64 in city centres, by contrast, arises from more deprived material and social living environments. However, these socioeconomic consequences of periurbanization fail to account for the urban mortality gradient observed among older people.