Crohn disease (CD) is a chronic inflammatory bowel disease which can cause transmural inflammation in a discontinuous distribution throughout the gastrointestinal (GI) tract from the oral cavity to the anus. CD has an often insidious presentation, with average time to diagnosis of roughly 5 months from onset of symptoms in children. Children with CD are most likely to present with abdominal pain, while other classical symptoms include weight loss, diarrhea, blood in the stool, perianal lesions, fevers, mouth ulcers, and arthralgias. The study of the genetics of CD in particular has yielded much evidence to support its role in the pathogenesis of the disease. Identification of the first, specific susceptibility locus, NOD2/CARD15 has led to phenomenal discoveries in the etiopathogenesis of CD. CD shows a basal plasmacytosis, transmural inflammation, and in roughly 20–40% of cases, a pathognomonic epithelioid granuloma. CD is a heterogeneous inflammatory disorder, which may affect any area of the body in addition to the GI tract.