The objective is to address the issue of uncertainty of causality in so-called medical cases, where an adverse outcome of treatment can be related to a combination of factors (medical error, the severe initial condition of the patient, etc.). A trend is observed to the significant increase in the number of favorable court decisions on patients’ claims for compensation for moral injury, even if forensic medical experts concluded that there was only an indirect link between defects in medical care and the adverse outcome. This approach by the courts is viewed critically and is due to, firstly, the absence in Russian law of special evidential theories in favor of the patient, allowing in certain cases (when medical records are improperly maintained, a gross error in treatment occurred, etc.) to determine the positive causality; secondly, this approach is related to use of the binary principle (yes/no) in deciding whether a causality exists instead of a proportional approach based on an assessment of probabilities. Given the significant «weight» of the expert opinion in the total body of evidence in a medical dispute, the practice of limiting the expert to answering that no conclusion can be drawn regarding causality without stating the most probable and rational explanation for the adverse medical outcome was criticized.