The domestic dog ( Canis familiaris) shows greater phenotypic variation than any other mammal. A corollary of this variation has been the recognition of more naturally occurring inherited diseases in dogs than have been cataloged in any other species apart from man. Recent catalogs list more than 370. A searchable Web-based database "Inherited Diseases in Dogs" (http://www.vet.cam.ac.uk/idid) has been developed. It catalogs diseases and conditions of dogs which are likely to be transmitted wholly or partly through a genetic mechanism, together with breeds in which they have been described. It contains disease listings and short descriptions, genetic and molecular genetic summaries where known, and connects to entry points to the literature on each disease.