Abstract: Objective and methods: For individuals who ruminate, or mentally rehearse past stressful events, the physiological effects of a stressor may be longer lasting. This is well-supported within the cardiovascular domain. In the context of the hypothalamic–pituitary–adrenal (HPA) axis and cortisol, the results are inconsistent. This review summarizes key theoretical and methodological issues that contribute to these mixed findings among the 15 studies to date that have examined the association between rumination and cortisol.Results: State measures of rumination were consistently linked to increased cortisol concentrations. Stress-related rumination questionnaires were often positively associated with cortisol, whereas depression-related rumination scales predicted lower cortisol concentrations or were unrelated to cortisol. Rumination manipulations in the laboratory (e.g., ruminative self-focused writing tasks compared to distraction writing tasks) influenced cortisol concentrations, but often did not increase cortisol relative to baseline values. Studies that utilized social-evaluative stressor tasks to examine the relationship between rumination and cortisol levels generally showed that rumination predicted greater cortisol reactivity or delayed recovery. Results from studies examining rumination and basal cortisol or the cortisol awakening response were inconsistent.Conclusion: The ways in which researchers conceptualize and assess rumination and the associated cortisol response influences the association between rumination and cortisol. Suggestions for future studies in this area of research are provided.