This invention provides methods of diagnosis and treatment of inflammatory bowel disease. In one embodiment, the invention provides methods of diagnosing and/or predicting susceptibility for inflammatory bowel disease in the Puerto Rican population by determining the presence or absence of a risk variant at the HPS1 locus. In another embodiment, the invention further provides methods of diagnosing and/or predicting protection against inflammatory bowel disease by determining the presence or absence of a protective variant at the IRF1 locus. In another embodiment, the presence in an individual of a risk variant at the CARD8 locus is diagnostic of susceptibility to Crohn's Disease in a Puerto Rican individual. In another embodiment, the presence of a risk variant at the TLR-9 locus in an individual is diagnostic of susceptibility to Crohn's Disease.