The responsibility of demographic isolation for the high incidence of genetic disorders among the population of the Saguenay region of Quebec, Canada, is explored. The authors reject the view that "a few family founders are the ancestors of most of the current population....Actually, between 1838 and 1911, more than 28,000 immigrants (representing one third of the number of births) settled in Saguenay, a major fact that has to be taken into account if one sets out to explain the genetic structure of this population, particularly if one considers that most of these immigrants came from the same region and were grouped in kin-related families." (SUMMARY IN ENG AND SPA)