Hypnotic relaxation therapy (HRT) has been shown to reduce hot flashes in postmenopausal women and breast cancer survivors. While the biological mechanism by which HRT reduces hot flashes is unknown, it has been speculated that reduction of stress mediates the intervention’s effectiveness. The purpose of the present study was to examine the effect of HRT on a known biomarker of stress (cortisol) and changes in cortisol as a mediator. Sixty-two postmenopausal women received hypnotic relaxation therapy for hot flashes and completed measures of hot flashes in addition to providing cortisol samples at baseline and endpoint. HRT resulted in significantly decreased early evening salivary cortisol concentrations. However, changes in salivary cortisol concentrations did not mediate the effects of HRT.