To compare the momentary association between salivary cortisol levels and pain, fatigue, and stress symptoms in patients with fibromyalgia (FM), and to compare diurnal cycles of cortisol secretion in patients with FM and healthy control subjects in a naturalistic environment.

Twenty‐eight patients with FM and 27 healthy control subjects completed assessments on salivary cortisol levels and pain, fatigue, and stress symptoms, 5 times a day for 2 consecutive days, while engaging in usual daily activities. Only those participants who adhered to the protocol (assessed via activity monitor) were included in the final analyses.

Twenty FM patients and 16 healthy control subjects adhered to the protocol. There were no significant differences in cortisol levels or diurnal cortisol variation between FM patients and healthy controls. Among women with FM, a strong relationship between cortisol level and current pain symptoms was observed at the waking time point (t = 3.35, P = 0.008) and 1 hour after waking (t = 2.97, P = 0.011), but not at the later 3 time points. This association was not due to differences in age, number of symptoms of depression, or self‐reported history of physical or sexual abuse. Cortisol levels alone explained 38% and 14% of the variation in pain at the waking and 1 hour time points, respectively. No relationship was observed between cortisol level and fatigue or stress symptoms at any of the 5 time points.

Among women with FM, pain symptoms early in the day are associated with variations in function of the hypothalamic–pituitary–adrenal axis.