Mesadenitis (mesenteric lymphadenitis, mesenteritis) is a common cause of acute abdominal pain syndrome in children. At the same time, the cause of acute mesadenitis is far from being established in all cases. Diagnosis of mesenteric lymphadenitis presents a certain problem. Differential diagnosis is always carried out with acute surgical diseases of the abdominal cavity, primarily with acute appendicitis. Special attention is paid to ultrasound examination in the diagnosis of mesadenitis. Given the absence of statistically proven diagnostic criteria for changes in abdominal lymph nodes in mesadenitis, it is relevant to determine their ultrasound characteristics. The article is presented in the form of a lecture for practicing pediatricians based on a literature review. The characteristics of mesentery lymph nodes in various pathological processes are collected from various sources. The features of ultrasound characteristics of mesenteric lymph nodes in normal and acute mesadenitis with herpes infection, coronavirus infection, tuberculosis, as well as features of lymph nodes with lymphogranuloma are presented. A table has been developed that indicates such characteristics as the shape, number of lymph nodes in the section, echogenicity, blood flow status, capsule, contour, as well as additional characteristics in some conditions (such as the tendency to form conglomerates or the presence of calcinates in the structure of lymph nodes in tuberculosis lesions). A detailed description of the lymph nodes makes it possible to conduct a preliminary differential diagnosis of mesadenitis using ultrasound, which makes it possible to determine the vector of further diagnostic search in children with acute abdominal syndrome, and then to select pathogenetically justified therapeutic tactics and preventive measures.