BACKGROUND: A flexible bronchoscope typically gets its designated size from the diameter of the distal tip but this is not the maximum diameter of the insertion tube. AIM: The aim of this study was to determine the size and site of the maximum diameter of flexible bronchoscope insertion tubes and to compare standard bronchofiberscopes with newer bronchovideoscopes. METHODS: We assessed 10 bronchoscopes ranging from 2.2 to 4.9 mm external diameter (Olympus, Tokyo, Japan) using an electronic digital caliper. Investigators were blinded to the type and model of each scope. The median, minimum and maximum diameters of the bronchoscopes were calculated and the measured diameters were compared with the stated diameters of the distal tip and insertion tube. RESULTS: The maximum and median measured diameters were wider than the stated diameter of the distal tip in all the scopes. The maximum discrepancy between the measured and stated diameters ranged from 0.19 mm (6.7%) to 0.66 mm (22.2%) with a mean of 0.41 mm (14.0%). There was no difference between bronchofiberscopes and bronchovideoscopes. CONCLUSION: The maximum diameter of the distal tip and insertion tube of pediatric sized flexible bronchoscopes is significantly greater than the manufacturer's specifications. This may impact on the choice of bronchoscope selected for procedures in children.