Comparative validation studies of pulse oximeters from different manufacturers have predominantly been performed in adult patients. However, due to differences in the patient-sensor interface, the results from those studies may not be transferable to the paediatric population. We therefore performed 123 simultaneous measurements (37 patients) of transcutaneous O2-saturation (StcO2) from 3 pulse oximeters and compared these with the arterial O2-saturation (SaO2) from a co-oximeter (Radiometer OSM 3). The median age of the 37 patients at the time of study was 2.0 months (range 1 day-5 years), their weight 4.7 kg (0.8-15.0 kg). The mean difference between StcO2 and SaO2 was -0.6% (SD 5.2%) for the Kontron 7840 pulse oximeter, -0.9% (SD 2.3%) for the Nellcor N200, and -1.2% (SD 3.5%) for the Radiometer OXI3 pulse oximeter. The corresponding 95% intervals were -7.4(-) + 9.6%, -5.7(-) + 4.3% and -7.0(-) + 6.3% for the Kontron, Nellcor and Radiometer instrument, respectively. These results demonstrate that neither of the 3 instruments systematically under- or overestimated SaO2. However, there were differences in precision, particularly in the low range of SaO2.