CROHN'S disease (CD) and ulcerative colitis are the major forms of chronic inflammatory bowel diseases in the western world, and occur in young adults with an estimated prevalence of more than one per thousand inhabitants¹. The causes of inflammatory bowel diseases remain unknown, but genetic epidemiology studies^2–5 suggest that inherited factors may contribute in part to variation in individual susceptibility to Crohn's disease. A genome-wide search performed on two consecutive and independent panels of families with multiple affected members, using a non-parametric two-point sibling-pair linkage method, identified a putative CD-susceptibility locus on chromosome 16 (P < 0.01 for each panel). The localization was centred around loci D16S409 and D16S419 by using multipoint sibpair analysis (ref. 6, and J.M.O., manuscript submitted) (P < 1.5 x 10⁻⁵). This region of the genome contains candidate genes which may be relevant to the pathogenic mechanism of inflammatory bowel diseases.