Inflammatory bowel disease (IBD) clusters within families, suggesting a genetic component to disease pathogenesis. Studies have identified a gene on chromosome 16cen that confers susceptibility to Crohn's disease. The affected gene codes for the NOD2/CARD15 protein, which is involved in the immune system's response to bacterial infection. Multiple mutations have been identified, three of which have been shown to be independently associated with Crohn's disease-arg702trp, gly908arg, and leu1007fsinsC. Taken together, these three variants confer a 15%-20% attributable population risk among cases of familial Crohn's disease, with decreased contribution among the more common sporadic cases of the disease. The presence of an NOD2 risk allele has been shown to be associated with ilial disease as well as an earlier age of disease onset. Further studies are needed to clarify the relationship between IBD genotype and disease behavior.