The purpose of this study was to assess the validity of salivary cortisol as an index of adrenocortical activity in older adults. Serum and salivary cortisol samples were collected in a sample of 36 healthy older adults (mean age = 66.64). The relationship of serum and salivary cortisol levels was assessed using correlation and regression analyses. In addition, the stability of serum and salivary levels over repeated samplings was assessed. The findings indicate that salivary measures of cortisol covary with serum levels, and both measures remain stable over repeated samplings. The utility of salivary cortisol as a marker of physiological reactivity is discussed. Future research is recommended to explore the emotional correlates of physiological reactivity in older adults.