This study examines the relative effects of population density and area-level SES on all-cause mortality in Denmark. A shared frailty model was fitted with 2.7 million persons aged 30–81 years in 2,121 parishes. Residence in areas with high population density increased all-cause mortality for all age groups. For older age groups, residence in areas with higher proportions of unemployed persons had an additional effect. Area-level factors explained considerably more variation in mortality among the elderly than among younger generations. Overall this study suggests that structural prevention efforts in neighborhoods could help reduce mortality when mediating processes between area-level socioeconomic status, population density and mortality are found.