The organization was founded in 1977 to locate children kidnapped during the repression, some of them born to mothers in prison who were later "disappeared", and to return the children to their surviving biological families. It was believed that at the time it was likely that around 30,000 had disappeared between the ages of 16-35; around 30% were women and of those women, around 3% were pregnant. The work of the Grandmothers, assisted by United States genetics scientist Mary-Claire King, had led to the location of more than 10 percent of the estimated 500 children kidnapped or born in detention centers, as well as identify almost seventy-one of those children which during the military era were illegally adopted, with their identities originally hidden.