['Patients with nonaneurysmal -subarachnoid hemorrhage (SAH) show either perimesencephal (pm)SAH or nonperimesencephalic (non-pm)SAH, with hemorrhage extending into adjacent cisterns. Patients with non-pmSAH have higher risk for a complicated clinical course with cerebral vasospasm (CVS) and worse outcome. Systemic inflammatory response has been linked to CVS occurrence and worse outcome in aneurysmal SAH. We analyzed whether levels of interleukin (IL)-6, a proinflammatory cytokine, differ in patients with pmSAH compared with non-pmSAH.', 'The clinical course with attention to symptomatic CVS occurrence and clinical outcome was assessed. Daily systemic IL-6 levels and leukocyte counts (Lc) were measured in the acute phase in 11 patients with pmSAH and in 9 patients with non-pmSAH.', 'Patients with non-pmSAH had significantly higher IL-6 levels compared to patients with pmSAH (14.7 ± 3.2 vs. 3.0 ± 0.6 pg/ml, p = 0.001). Lc counts did not differ (11.5 ± 0.5 vs. 11.2 ± 0.6 × 10(3)/μl, p = 0.485). Patients with non-pmSAH stayed significantly longer in the neurocritical care unit (16.4 ± 2.1 vs. 10.2 ± 1.1 days, p = 0.012). Symptomatic CVS occurred in two patients with non-pmSAH. Patients with pmSAH had a significantly more favorable outcome, defined as Glasgow Outcome Scale 5.'] Do systemic interleukin-6 levels reflect illness course and prognosis of patients with spontaneous nonaneurysmal subarachnoid hemorrhage?