Thermography is an imaging technique that records the infrared radiation of the skin with a potential to detect asymmetries in body temperature and relating them to pathologies or risk of injury. However, the location of landmarks and region of interest (ROI) can influence the recording process. In this study we describe the reliability of a method to select the ROI without modifying the original thermogram over 68 thermograms (17 participants) of patellar tendon with an infrared camera (softwareOptris 450PI). The width-height, X-Y axis and mean temperature of the ROI was measured by two examiners.All the lower limits of the Intraclass Correlation Coeficiente (CCI) were over 0.84 without biases. The skin temperature was similar for both intra-examiner (F1,33=0.488; p=0.490) and inter-examiner (F1,33=0.011; p=0.917). The mean differences were 0.006ºC (Limit of agreement (LoA): -0.10 to 0.10), The differences between examiners were 0.001 ºC (LoA: -0.13 to 0.13). All temperature differences were <0.25ºC. The method used has very good intra and inter-examiner reliability and reproducibility and the influence on the skin temperature is negligible. It will be of interest to extend the study to ascertain the reliability using different thermal cameras and software, which could increase the strength of the method.