Some diseases, especially at the early stage of their development, mimic infectious diseases. This is mainly due to the nonspecific character of the symptoms that characterize the initial manifestations of intoxication syndrome: fever, torpidity, weakness, loss of appetite, etc. Quite often, such symptoms as vomiting or frequent bowel movements, sometimes thin stool may appear in children as a response to these symptoms. The danger of these states that it is often takes time to identify the causes of these manifestations of the disease, which allows the true pathological process to gain momentum, which sometimes makes it an irreversible and irreparable. As an example we present a clinical case of a 6-year-old child with phlegmonous appendicitis.