There is a broad spectrum of presentations and severity of necrotizing enterocolitis. Because it may have several different causes, ncerotizing enterocolitis may be a syndrome rather than a specific disease. The triad of formula feeding, intestinal ischemia, and bacterial growth may be part of the pathogenesis of necrotizing enterocolitis. Bacteria are of central importance for the production of pneumatosis, a prerequisite of which is formula feeding. Bacteria may also contribute to the intestinal injury seen after ischemia. However, the disease in the low risk patient seen during an epidemic associated with a single organism is probably caused by a primary gastrointestinal infection. On the other hand, in the stressed newborn infant with mucosal injury the presence of the appropriate bacteria may be all that is needed to initiate the chain of events leading to necrotizing enterocolitis. Figure 2 illustrates the importance of bacteria in all the causes proposed to be involved in the pathogenesis of necrotizing enterocolitis. Whether bacteria are primary or secondary agents, necrotizing enterocolitis should always be approached therapeutically as an infectious disease.