Elevated intestinal nitric oxide (NO) is one of the common findings in NEC. NO plays important roles in normal physiology and pathophysiology of the neonatal intestine. Low levels of NO produced under normal conditions by endothelial and neuronal NO synthases homeostatically regulate intestinal motility, mesenteric blood supply, blood clotting, intestinal electrolyte secretion, endothelial permeability, and gut barrier function in a manner dependent on cGMP and cGMP-activated protein kinase PKG1. High levels of NO produced during intestinal inflammation by inducible NO synthase increase permeability of endothelial and gut barriers via S-nitrosylation and nitration of proteins. High levels of NO are likely to also affect processes mediated by the cGMP-PKG1 pathway. In NEC, NO elicits both pathogenic and protective effects, complicating therapeutic targeting of this molecule.