BACKGROUND We compared Nexfin non-invasive arterial pressure measurements using a novel small finger cuff with intra-arterial pressure in the paediatric setting in order to establish the level of agreement between both methods. METHODS The study included 41 children aged 2-16 yr admitted for surgery or paediatric intensive care with an intra-arterial catheter as part of standard monitoring. Values of systolic (SAP), diastolic (DAP), and mean arterial pressure (MAP) were obtained simultaneously from the intra-arterial catheter and the non-invasive Nexfin monitor. Data were analysed using intra-class correlation (ICC) coefficients and the Bland-Altman analysis. RESULTS A non-invasive arterial pressure signal was obtained in the majority of patients. The reproducibility of arterial pressure measurements over time by both non-invasive and invasive techniques was high, with ICC coefficients ranging from 0.94 to 0.98. The Bland-Altman analysis for SAP, DAP, and MAP revealed a bias with 95% limits of agreement of -13.5 (-39.7; +12.8), -0.2 (-12.8; +13.2), and -2.6 (-17.7; +12.5) mm Hg, respectively. Linear regression suggested a weak correlation of SAP and the bias between intra-arterial and Nexfin SAP measurements (intercept 4.9 mm Hg, β -0.29; P=0.01). CONCLUSIONS Nexfin non-invasive arterial pressure measurements are feasible in paediatric patients. Nexfin accurately reflects the intra-arterial MAP and DAP curves, but seems to underestimate SAP compared with intra-arterial pressure. These results suggest that Nexfin may be used in low-to-moderate risk children without severe systemic hypotension, who require beat-to-beat haemodynamic monitoring but do not have an indication for invasive measurements.