In this study, associations were examined between cortisol levels of wives and husbands in 47 heterosexual married couples. Both partners’ salivary cortisol levels were measured at the same moments seven times a day on 2 typical weekdays. After accounting for the effects of the diurnal rhythm of cortisol and relevant control variables, dyadic hierarchical linear modeling indicated significant positive linkages between partners’ cortisol levels, consistent with the hypothesized within‐couple physiological synchrony. Variables reflecting more (spousal presence) or less connectedness (loneliness, being alone) were also collected at the time of each cortisol sample. Results indicated that husbands’ cortisol levels were higher at moments they reported feeling lonelier and lower at moments they were in the presence of their spouse. Wives’ cortisol levels were higher at moments they were alone. In addition, wife–husband cortisol synchrony was stronger for husbands who spent relatively more time with their spouse across the study period—even after accounting for time spent with others in general. These findings suggest that marital partners evidence positive within‐couple cortisol associations, and that connectedness (particularly physical closeness) may underpin spouses’ physiological synchrony.