The periodontal probe is still the most important tool for a correct and reproducible periodontal diagnosis. The aim of this study was to verify the standardisation from millimeter marks and tip diameter of four currently marketed periodontal probes. 129 new probes were randomly acquired in the market: 9 Williams-Hu Friedy (group A), 50 Williams-Golgran (group B), 35 Williams-Neumar (group C) and 35 WHO-Hu Friedy (group D). Mark calibration was assessed by digital images that were analysed by an image analysis system. A digital caliper assessed the tip diameter. Blind duplicate measurements were undertaken. The calibration of mark measurements demonstrated that all probes used in this study were not precise, although groups A and D were more accurate than groups B and C (P < 0.05). The tip diameter analysis did not reveal significant differences among the groups (P > 0.05). It can be concluded that some concern should arise regarding the standardisation of periodontal probes since they are relevant to minimise probing errors and consequently enhance the accuracy and reproducibility of periodontal probe-dependant measurements in clinical and epidemiological studies.335760