Although a broad spectrum of entities can induce acute pathologic changes in the small bowel, there are relatively few imaging features that are characteristic of a specific diagnosis on the basis of CT findings. Specific clinical information, including time course and onset of disease, patient risk factors, and any recent pharmacologic or radiation therapy, is often instrumental in refining the differential diagnosis. A wide spectrum of disorders is reviewed in this article; however, given the breadth of disorders associated with the small bowel, neoplastic and infectious conditions affecting the small bowel that can manifest acutely are not specifically discussed. Vascular diseases that can affect the small bowel regionally or diffusely, including thromboembolic and hypoperfusion phenomena, as well as a spectrum of vasculitides, are reviewed. Iatrogenic causes of small bowel disorders are discussed, including angiotensin-converting enzyme inhibitor–induced angioedema, and chemotherapy-and radiation therapy–associated patterns of disease. Autoimmune and hereditary conditions that can affect the small bowel, including systemic lupus erythematosus and genetic C1 esterase inhibitor deficiency, respectively, are reviewed.