BACKGROUND & AIMS: Familial aggregation argues for genetic susceptibility to Crohn’s disease. The aim of this study was to compare the age of onset and the clinical features of Crohn’s disease between patients with familial disease and those with sporadic disease and investigate the concordance for disease location and type among relatives with Crohn’s disease. METHODS: Seventy-two families with 2 (n = 55), 3 (n = 8), 4 (n = 6), and 5 or more (n = 3) affected first-degree relatives were selected for the study. A population of 1377 patients with sporadic nonfamilial Crohn’s disease was used for comparison. RESULTS: Clinical data were obtained from 176 patients with familial Crohn’s disease (79 men and 97 women). Median age at onset was younger in familial Crohn’s disease than in sporadic cases: 22 vs. 26.5 years (P < 0.01). In familial cases, fewer patients had exclusively colonic involvement and more patients had both small bowel and colonic involvement. Among relatives of families with 2 affected members, 56% were concordant for disease location and 49% for disease type. These percentages reached 83% and 76%, respectively, within families with more than 2 affected members. CONCLUSIONS: Patients with familial Crohn’s disease are characterized by an early age at onset with more extensive disease and may represent a homogeneous clinical subgroup with a particularly strong genetic influence.