The purpose of this prospective observational study was to investigate the relation between the frequency of critical neuromonitoring parameters (brain tissue pO2, (PtiO2) < or = 10 mmHg, intracranial pressure (ICP) > 20 mmHg, cerebral perfusion pressure (CPP) < or = 70 mmHg) and outcome after severe aneurysmal subarachnoid hemorrhage (SAH). In a prospective study on 42 patients monitoring of ICP, CPP, and PtiO2 (in the area at risk for vasospasm) was performed. All patients were primarily classified as Hunt and Hess grade 4 or with secondary deterioration to this grade. Relative proportions of PtiO2 < or = 10 mmHg (n = 42), ICP > 20 mmHg (n = 25) and CPP < or = 70 mmHg (n = 23) were derived from multimodal neuromonitoring data sets for different time intervals, i.e. 1. the total monitoring time; 2. the total monitoring time without the last two monitoring days; 3. the second last monitoring day; and 4. the last monitoring day. Patients were divided into nonsurvivors (GOS = 1) and survivors (GOS = 3-5). For the total monitoring time, significant differences in the relative proportion of critical values were found for all neuromonitoring parameters (p < 0.05). The detailed analysis of consecutive time intervals revealed significantly increased proportions of critical values in nonsurvivors for all neuromonitoring parameters during the last day only. Additionally, ICP > 20 mmHg was significantly more frequent during the second last day (p < 0.01). For other time periods no differences were observed. We conclude, that critical neuromonitoring values are not early predictors of nonsurvival in patients suffering from severe SAH.