BACKGROUND The purpose of this study was to investigate the relationship between continuously monitored regional cerebral blood flow (CBF) and brain tissue oxygen (PtiO2). METHODS Continuous advanced multimodal neuromonitoring including monitoring of PtiO2 (Licox, GMS) and CBF (QFlow, Hemedex) was performed in eight patients after severe subarachnoid haemorrhage (n=5) and traumatic brain injury (n=3) for an average of 9.6 days. Parameters were measured using a flexible polarographic PtiO2-probe and a thermal diffusion CBF-microprobe. RESULTS Regarding the whole monitoring period in all patients, the data indicated a significant correlation between CBF and PtiO2 (r=0.36). In 72% of 400 analysed intervals of 30 minutes duration with PtiO2 changes larger than 5 mmHg, a strong correlation between CBF and PtiO2 existed (r>0.6). In 19% of intervals a still statistically significant correlation was observed (0.3<r<0.6). During the remaining 9% no correlation was found (r<0.3). Regarding the clinical stability of the monitoring devices, the CBF monitoring system allowed monitoring of CBF in 64% of the time when PtiO2 monitoring was possible only. Phases of non-monitoring were mostly due to fever of the patient, when the system does not allow monitoring to avoid overheating of the cerebral tissue. CONCLUSIONS This study suggests a correlation between CBF and PtiO2. The level of PtiO2 seems to be predominately determined by regional CBF, since changes in PtiO2 were correlated in 90% of episodes to simultaneous changes of CBF.