BACKGROUND: A standardized examination procedure and correct bowel wall assessment are the prerequisites for correct findings and for distinguishing normal findings from pathological diagnoses. PubMed was searched for the time period from January 01, 1990 - March 29, 2024, using a Boolean search Summary: The present work provides knowledge and details of the examination of the gastrointestinal tract in transcutaneous ultrasound with examination procedure, transducer selection, transducer guidance, knowledge of the identification of anatomical structures and sonographic assessment. The sonographic reference values for the gastrointestinal tract were researched, compiled, and interpreted. In addition, citations and references of eligible studies were searched to identify further studies for inclusion. KEY MESSAGES: Knowledge of the sonographic appearance of the gastrointestinal tract and the standardized examination of the healthy gastrointestinal tract, including correct measurements, must be trained. Although age, body weight and food ingestion influence the thickness of the intestinal wall, it does not normally exceed 2 mm in the duodenum, jejunum, ileum and colon on US. However, in most clinical studies 3 mm was used as cut-off for pathology. When assessing the appendix, an outer diameter of <
6 mm is considered normal. However, an increase in this diameter may also occur in healthy, asymptomatic people and should be not used as the sole criterion for diagnosing appendicitis. GIUS is now established as valid clinical method to assess patients with digestive diseases. Accordingly, there is a great need for training opportunities and supervision of young doctors who want to enhance their knowledge and skills in GIUS.