The 45-years-old men, who were born deaf, spent their lives side-by-side growing up together and then, as adults, sharing an apartment and working as cobblers together, according to Belgian media reports.
The men's names have not been released but photographs of the identical twins from the Antwerp region have been made available to some media outlets.
Their doctor, David Dufour, told Belgium's RTL Television over the weekend that the two men had been losing their eyesight for several years and soon would have been completely blind. The prospect of being blind as well as deaf was unbearable to them, he said.
"They were fully aware of their decision," Dufour said.
After winning approval from the necessary authorities, the two men received lethal injections at a Belgian hospital in December.
Dufour described their last moments: "They had a last cup of coffee and everything was fine. They said goodbye to their parents and brother and all was serene. They waved and that was that."
Under a 2002 law, Belgians are allowed to end their own lives if a doctor judges an individual has made his or her wishes clear and is suffering unbearable pain.
The case of the twins was unusual because the two men were not approaching the end of their natural lives nor were they terminally ill.
But Jacqueline Herremans, a member of the Belgian Commission of Euthanasia, told RTL that they did meet the legal requirements as their suffering was grave and incurable.
When they became blind as well as deaf, he said, they would not have been able to lead autonomous lives, and that with only a sense of touch they had no prospects of a future.
She acknowledged this was an exceptional case.
"Evidently they had a particular destiny. They were two human beings who have lived together, grown up together, worked together and wanted to die together. Their suffering may not have been physical, but there was psychological suffering," she said.
In 2010 and 2011, a total of 2,086 people died by euthanasia in Belgium, according to the country's Euthanasia Commission.
Belgium is now looking at introducing a legal amendment that would allow children and those with dementia the option of seeking permission to die. If passed later this year, the option of euthanasia will be extended to minors affected by an incurable illness, or suffering that cannot be alleviated.
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