The cerebral tissue oxygenation index (TOI) and fractional tissue oxygen extraction (FTOE) reflect the cerebral oxygenation. We studied the effect of glycaemia on the TOI and FTOE, as measured by near-infrared-spectroscopy (NIRS). We continuously measured TOI, glycaemia, mean arterial blood pressure (MABP), saturation (SaO(2)) and transcutaneous carbon dioxide pressure (tPCO(2)) for at least 4 h during the first week of life in neonates with gestational age (GA) < 32 weeks and weight < 1500 g. FTOE was calculated. 24 measurements in 11 neonates were analyzed. We found a significant negative correlation (r = -0.077; p = 0.0344) between glycaemia and TOI, also after correction for MABP, SaO(2) and tPCO(2) (r = -0.118; p = 0.002) and a significant positive correlation between glycaemia and FTOE (r = 0.147; p < 0.000) which remained significant after correction for MABP and tPCO(2) (r = 0.116; p = 0.001). Our results indicate that in neonates during the first days of life glycaemia - even within the normal ranges and after correction for MABP, SaO(2) and tPCO(2) - influences the cerebral oxygenation.