This paper is devoted to the analysis of expert errors made in the course of implementation of the Medical Criteria for the estimation of the severity of harm to human health. In 2010, the Moscow Regional Bureau of Forensic Medical Expertise issued 11 180 primary expert judgments and acts of forensic medical examination of the total number of 26 196 expertises performed (43%). They include 2797 cases of severe harm to health, 2881 cases of moderate and 5502 cases of mild harm to health. Only 74 (1.3%) of the 5678 cases of severe and moderate harm to health were misinterpreted by the experts. Thirty three (0.6%) judgments were considered as doubtful. Sixty one of the 74 cases of harm to health were erroneously described as severe and 13 ones as moderate. The main source of the errors was misapplication of the respective articles of the Medical Criteria for the estimation of the severity of harm to human health. Only 20 (0.4%) of the 5502 cases estimated as mild harm to health proved erroneous. Fifty four (1%) judgments were recognized to be doubtful. A total of 264 forensic medical expertises were performed by expert commissions during 2010 of which 118 (45%) were designed to estimate the harm to human health. In more than two thirds of the cases, the errors of primary expertise of the severity of harm to human health due to the misapplication of the Medical Criteria were either revised or corrected; the remaining one third of the judgments were left unaltered (i.e. the results of the primary expertise were confirmed).