SummaryWe evaluated the near-infrared spectroscopy based tissue haemoglobin index for continuous non-invasive monitoring of haemoglobin concentration during paediatric surgery. Blood samples from 40 children (from birth to 16 years old) were analysed oximetrically. From the first blood sample the tissue haemoglobin index ⁄ haemoglobin concentration coefficient was calculated for further tissue haemoglobin index-derived haemoglobin concentrations in each patient. Comparison of corresponding values revealed a bias and precision of -0.02 and 5.41 g.l )1 , respectively.Sensitivity and specificity of tissue haemoglobin index were 73.1% and 70.0%, respectively, for predicting falling haemoglobin concentration values. Currently, the tissue haemoglobin index is not suitable for monitoring haemoglobin concentration in children undergoing surgery.