The purpose of this study was to assess cortisol dynamics in the acute phase after aneurysmal subarachnoid hemorrhage (SAH) and to set the parameters of cortisol release in relation to the severity of illness and outcome. In 22 consecutive patients with aneurysmal SAH, cortisol, corticosteroid binding globulin, interleukin-6, and adrenocorticotrophic hormone were measured immediately after hospital admission (t(0)), 7 days (t(1)) later, and at least 14 days later (t(2)). Additionally, diurnal profiles of cortisol secretion were assessed at t(1) and t(2), and area under the curve (AUC) was computed for calculated free serum cortisol (CFSC). In this study, normal diurnal CFSC profiles were associated with a significantly shorter ICU-stay, less complications, and a more favorable outcome than abnormal diurnal profiles. AUC and 8 a.m. cortisol were not related to clinical course or outcome. It is concluded that cortisol secretion patterns are associated with the severity and outcome of SAH. For an appraisal of the hypothalamo-pituitary-adrenal axis in SAH patients, single cortisol measurements are insufficient.