Upper gastrointestinal obstruction (UGIO), obstruction occurring at the level of the stomach or duodenum, represents only about 5% of bowel obstructions. As with other bowel obstructions, timely diagnosis is necessary to prevent complications including ischemia and death. Because the presenting symptoms of UGIO can be vague and nonspecific, the diagnosis may not be suspected clinically. The radiologist therefore provides immense value as the diagnosis and often the etiology of the obstruction can be ascertained through imaging. Here we present a simple classification scheme of etiologies of UGIO into congenital, malignant, infectious/inflammatory, and mechanical categories, and provide examples of the most common and some uncommon causes for each category. We highlight that several of the congenital etiologies of UGIO can present at any age, including adulthood, and therefore it is important for the radiologist to keep these diagnoses in mind when reviewing cases of UGIO. For each etiology, we provide typical imaging strategies that are used for diagnosis as well as key points regarding the diagnosis.Copyright © 2020 Elsevier Inc. All rights reserved.