OBJECTIVE: Fibromyalgia has been characterized as a basic disorder of endocrine stress responses in which psychological stress has been linked both with etiology and symptom severity. This study investigated associations of religiosity and spirituality with psychological and physiological (endocrine) measures of stress in a sample of women with fibromyalgia. METHOD: Ninety-one participants provided self-reports of religiosity and spirituality using the Duke University Religion Index (DUREL) and the Index of Core Spiritual Experiences (INSPIRIT). Psychological outcomes were measured with the Perceived Stress Scale (PSS), and diurnal salivary cortisol profiles were measured as an indicator of neuroendocrine regulation. RESULTS: Hierarchal regression analyses controlling for age and medications likely to affect cortisol levels revealed significant associations of nonorganizational religiosity and intrinsic religiosity with the diurnal cortisol rhythm. Patients reporting medium or high religiosity had rhythmic cortisol profiles characterized by high morning and low evening levels. In contrast, cortisol rhythms of those reporting low religiosity appeared flattened. The association between intrinsic religiosity and cortisol rhythm persisted after controlling for social support. No significant effects of religiosity or spirituality on perceived stress were observed. CONCLUSIONS: These data suggest that religiosity may have a protective effect on the physiological effects of stress among women with fibromyalgia.