Three doctors will face a criminal trial in Belgium accused of failing to comply with the legal conditions for euthanasia, the first such case since it was decriminalised in 2002.
"This is the first time that there has been a decision to refer such a case to a court of law," lawyer Jacqueline Herremans said.
"There have already been legal cases involving doctors, but they have always resulted in dismissals before going to court," added Herremans, who chairs the Belgian Association for the Right to Die with Dignity.
The case follows the announcement that Dutch authorities are prosecuting a doctor for euthanising an elderly woman with dementia in the first case of its kind in neighbouring the Netherlands.
Belgium and the Netherlands became the first countries in the world to legalise so-called mercy killing, but it can only be carried out by doctors and under very strict conditions.
The decision in Belgium, taken on Thursday by the Court of Appeal in Ghent, stems from a civil action brought by a sister of an autistic woman, Tine Nys, who was euthanised in 2010 at the age of 38.
The sister accused the doctors of not having properly prepared the case and of taking a rushed decision when the woman had not been treated for mental issues for years.
The diagnosis of autism had only been made two months before her death, according to the Belgian media.
In Belgium, euthanasia has been allowed since 2002 for patients suffering from an incurable disease who have made their request "voluntarily, thoughtfully and repeatedly".
This right for adults was extended in 2014 to minors, within an equally strict legal framework.