Infrared Thermography (IRT) was introduced to medicine in 1956 by the Canadian surgeon Lawson as a promising modality for diagnosing breast cancer. It became quickly obvious, that IRT does not give much anatomical/morphological information but provide an easily obtainable map of measurable skin temperatures. Consequently, extracting temperatures from thermal images became the standard method of analysis in medical thermography. However, the awareness of errors in obtained measurements did develop quite slowly. In 2017, a checklist was developed in a Delphi process to address conditions that should be reported in thermographic studies since they could affect thermography-based temperature readings. These potential sources of uncertainty include individual data of participants and their preparation for thermal imaging; extrinsic factors such as recent physical activity or physiotherapy; wetness of the skin; ambient temperature, humidity and infrared sources in the examination space; acclimation time; camera type, camera settings, emissivity; size of field of view; camera position in relation to the imaged subject; image analysis. Presented are examples of the magnitude of uncertainties caused by the camera performance, size of the field and angel of view and size and position of regions of interest. Due to the manifold of possible uncertainties in clinical thermography, the use of high thresholds for clinical meaningful temperature differences are recommended.