Poor sleep is often independently associated with greater pain sensitivity and dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis (e.g., greater basal cortisol and exaggerated stress-induced cortisol reactivity). However, the interactions among sleep, pain, and the HPA axis have not been adequately evaluated. In this study, 40 healthy adults provided self-report regarding perceived sleep quality over the past month prior to completion of an acute noxious physical stressor (i.e., cold pressor task; CPT). Following the CPT, they reported on the severity of pain experienced. Salivary cortisol was sampled before, immediately following, and during recovery from CPT. Using bootstrapped confidence intervals with a bias correction, results showed that poor sleep quality was significantly associated with greater reports of CPT-induced pain severity and greater cortisol reactivity (i.e., increase from baseline). Furthermore, greater cortisol reactivity to the CPT was found to significantly mediate the relationship between poor sleep and pain severity. © 2012 Elsevier B.V.