At present, various scar assessment scales are available, but not one has been shown to be reliable, consistent, feasible, and valid at the same time. Furthermore, the existing scar assessment scales appear to attach little weight to the opinion of the patient. The newly developed Patient and Observer Scar Assessment Scale consists of two numeric scales: the Patient Scar Assessment Scale (patient scale) and the Observer Scar Assessment Scale (observer scale). The patient and observer scales have to be completed by the patient and the observer, respectively. The patient scale's consistency and the observer scale's consistency, reliability, and feasibility were tested. For the Vancouver Scar Scale, which is the most frequently used scar assessment scale at present, the same statistical measurements were examined and the results of the observer scale and the Vancouver scale were compared. The concurrent validity of the observer scale was tested with a correlation to the Vancouver scale. Furthermore, the authors examined which specific characteristics significantly influence the general opinion of the patient and the observers on the scar areas. Four independent observers have each used the observer scale and the Vancouver scale to assess 49 burn scar areas of 3 x 3 cm belonging to 20 different patients. Subsequently, the patients completed the patient scale for their scar areas. The (internal) consistency of both the patient and the observer scales was acceptable (Cronbach's alpha, 0.76 and 0.69, respectively), whereas the consistency of the Vancouver scale appeared not to be acceptable (alpha, 0.49). The reliability of the observer scale completed by a single observer was acceptable (r = 0.73). The reliability of the Vancouver scale completed by a single observer was lower (r = 0.69). The observer scale showed better agreement than the Vancouver scale because the coefficient of variation was lower (18 percent and 22 percent, respectively). The concurrent validity of the observer scale in relation to the Vancouver scale is high (r = 0.89, p < 0.001). Linear regression of the general opinions on scars of the observer and the patient showed that the observer's opinion is influenced by vascularization, thickness, pigmentation, and relief, whereas the patient's opinion is mainly influenced by itching and the thickness of the scar. Such an impact of itching and thickness of the scar on the patient's opinion is an important and novel finding. The Patient and Observer Scar Assessment Scale offers a suitable, reliable, and complete scar evaluation tool.