Many clinicians broadly classify intestinal ischemia into acute or chronic disease. However, because certain acute events may change to a chronic condition, a clear-cut classification of ischemic bowel disease using this two-category system is not always applicable. Since the extent of intestinal ischemia and the pathological consequences depend on the size and the location of the occluded or hypoperfused intestinal blood vessel(s), we find it useful to classify ischemic bowel disease according to the size and type of the vessel(s) that are hypoperfused or occluded (Figure 1). Accordingly, intestinal ischemia may result from occlusion/hypoperfusion of a large mesenteric vessel (mesenteric artery or vein) or from occlusion/hypoperfusion of smaller intramural intestinal vessels. In each of these situations the resultant intestinal ischemia may be acute or chronic. In addition, it is important to point out that vessel occlusion/hypoperfusion may be the result of a mechanical intraluminal obstruction (i.e., embolus or thrombus) or the result of decreased blood flow due to vasospasm, increased blood viscosity, hypotension or other similar conditions. The latter is referred to as nonocclusive ischemia. Therefore, the etiology of vessel occlusion/hypoperfusion may be the basis for subclassification of ischemic bowel disease. A clinically important further classification is whether the ischemia-induced necrosis is transmural (gangrenous ischemia) leading to peritonitis, or remains intramural (nongangrenous ischemia) resulting in localized disease. Figure 1 attempts to combine these different aspects of subdivision in a comprehensive classification.