The author discuss the problematics of the ultrasonographic picture of diseases causing the right lower quadrant pain with regard to specific features of child age. The author describes the correct sonographic examination method, changes which can be observed on sonography and discuss diagnostic possibilities and limitations of the method while the emphasis is given on the analysis of morphologic and pathological changes developed by these conditions. Though the main attention is logically focused on acute appendicitis, the other important conditions simulating appendicitis in child age and which have to be considered in the differential diagnosis (as mesenteric adenitis, either as a separate unit or in combination with inflammation in the region of caecum and ileum, ileo-ileal invagination, inflammation of Meckel’s diverticulum, Crohn’s disease, etc.) are described as well. The author also compares sonography with computed tomography within the framework of diagnostic capabilities in relationship to acute appendicitis.

        Key words: ultrasonography, acute appendicitis, acute abdomen, alternative diagnosis, mesenteric lymphadenitis, inflammation of the terminal ileum and ileocaecum, invagination