Many mentally handicapped Danes, including children, were lobotomised between 1947 and 1983, and many died from the operation, a historian behind a soon-to-be-published book on the topic told Danish media Thursday.
"Doctors did not count on curing them completely, but wanted to pacify them, perhaps to better their condition," Jesper Vaczy Kragh told the Christian daily Kristelig Dagbladet.
"The results of such operations generally were not good, and some 7.6 percent did not survive," said the medical historian, behind a book on lobotomies set to be published in October.
"What happened with people with mental handicaps is worse than what happened with psychiatric patients," he said, referring to many operations performed on children as young as six years of age, even though their brains were not yet completely developed.
Official figures show that between 1947 and 1983, when conducting lobotomies was outlawed in Denmark, around 4,500 Danes had the operation.
But it was previously unknown that many mentally handicapped people were subjected to the procedure.
Kragh estimates more than 300 mentally handicapped people were operated on during that period at Copenhagen's University Hospital and at a municipal hospital in Aarhus, Denmark's second largest city.
The president of LEV, the national association of handicapped people, Sytter Kristensen, said she was deeply shocked by the revelation.
"Those were highly educated people (doctors) who were taking advantage of defenseless people without being sure of having the slightest positive result," she told Kristelig Dagbladet.
Health Minister Bertel Haarder said he thought it was good to shine the spotlight on the cases.
"The explanation is that, for a long time, mentally handicapped people were not regarded as equal. Their lives were considered to be without value," he said.
Explore further: Understanding psychosis and schizophrenia