OBJECTIVE The association of genetic influences between bowel location and clinical type of Crohn's disease may provide more information on the genetic heterogeneity of inflammatory bowel disease. The aim of this study was to analyze familial occurrences of Crohn's disease for concordance for site and type. METHODS Of 554 consecutive patients, 95 (17%) had a family history of Crohn's disease. Sixty families were analyzed for concordance for site and clinical type and by a series of conditional logistic regression models to test the significance of concordance within families. RESULTS Eighty-six percent of families were concordant in at least 2 members for the site of Crohn's disease, and 82% were concordant for clinical type. Pairing family members together, concordance greater than expected in an unrelated population was observed. Using a conditional logistic regression model, a statistically significant role for concordance in predicting site and type of Crohn's disease in other affected family members was found. CONCLUSIONS Greater-than-expected concordance for site and clinical type of Crohn's disease within individual families is compatible with a concept of multiple, distinct forms of Crohn's disease, which, although possibly influenced by environment, seem more likely to be separate inheritable forms or phenotypes.