Social support is associated with better health but it is unknown whether the health advantages of social support depend on the support source. Using a probability sample of older U.S. adults (n=1430) we compared leukocyte telomere length, a biomarker of cellular aging, between married adults whose support sources either did or did not include their spouse. Despite having social support from other sources, participants who lacked spousal support had shorter telomeres relative to those with spousal support. The size of this telomere difference was comparable to differences between men and women and was independent of sociodemographic variables, coronary heart disease risk, diagnosed chronic disease and other social relationship resources such as the number of support sources, the number of friends, or the availability of financial support. Our findings suggest that relative to other sources of social support, spousal support may be especially important for cellular aging, a general biological mechanism that is implicated in age-related chronic disease risk.