The article presents the possibilities of virtual diagnosis of a clinical case — a child with bone pain when walking and signs of rickets. The purpose of this work is to demonstrate the use of the case method for teaching the diagnosis of orphan diseases on a specific example. The authors have developed a web application that allows you to check the correctness of the actions of a trained doctor at each step of virtual diagnostics. The doctor must analyze the information provided about the patient, determine a plan for further examination, «refer» the patient for consultations with specialists and choose which diseases need to be differentiated. In the process of virtual diagnostics, questions are provided that allow you to assess the correctness of the choice of actions, to explain what the mistake is in case of an incorrect decision in a particular situation. As a result of passing the case, an integral score is calculated and displayed on the screen — the sum of points for correct answers. The ability to increase this score motivates the doctor to re-undergo virtual diagnostics, and most importantly, helps to consolidate the knowledge necessary for the correct diagnosis. Educational material is also provided: video presentations on various aspects of the identified disease, as well as an animated video on the molecular mechanisms underlying the pathogenesis. The knowledge control block includes questions on the training material, as well as graphic tests for the placement of information blocks, ranking and compliance. An interactive clinical case can be used in the process of training medical students and clinical residents as an additional tool, as well as for advanced training of pediatricians, nephrologists, endocrinologists and doctors of other specialties who may encounter this pathology in their practice. The developed Internet resource is posted on the Educational Portal of the Veltischev Institute https://edu.pedklin.ru.