There is growing evidence that there are stable and meaningful individual differences in how much people vary in their experience of positive affect (PA), which in turn may have implications for health and well-being. Does such PA variability play a role in physiological processes potentially related to stress and health, such as daily cortisol profiles? We explored this question by examining whether PA variability across and within days in middle-aged adults (Study 1) and across weeks in older adults (Study 2) was associated with daily salivary cortisol profiles. In both studies, individuals who exhibited moderate PA variability demonstrated more favorable cortisol profiles, such as lower levels of cortisol and steeper slopes. Interestingly, for middle-aged adults (Study 1), high levels of within-day PA variability were associated with the least favorable cortisol profiles, whereas for older adults (Study 2), low levels of across-week PA variability were associated with the least favorable cortisol profiles. Collectively, these findings provide some of the first evidence that PA variability is related to daily cortisol profiles, suggesting that it may be better to experience a moderate degree of positive affect variability. Too much or too little variability, however, may be problematic, potentially carrying negative implications for stress-related physiological responding.