Families of patients who die by euthanasia cope better than those of patients who die by natural causes, say researchers.
Relatives of patients who died naturally displayed more symptoms of grief
Dutch researchers say they have fewer symptoms of grief and post-traumatic stress disorder because they have had the chance to say goodbye.
The team stress they are not advocating euthanasia. But they say their research does indicate that it does not increase the grief felt by families, as was previously thought.
UK bereavement experts said the ability to say goodbye was recognised as helping relatives and friends cope with the death of a loved one.
Euthanasia is legal in the Netherlands. It is not legal in the UK.
The researchers sent questionnaires to 189 bereaved family members and close friends of terminally ill cancer patients who died by euthanasia and 316 bereaved family members and close friends of comparable cancer patients who died a natural death between 1992 and 1999.
They asked them about symptoms of grief, post-traumatic stress and depression.
The family and friends of the patients who died by euthanasia had less traumatic symptoms than the group whose relatives died through natural causes.
The researchers say this is likely to be because, in addition to saying goodbye, they could be more prepared for their loved one's death and more able to talk openly about what was going to happen and how they would feel.
Dr Nikkie Swarte of the University Medical Center in Utrecht, the Netherlands, told BBC News Online: "This is not a plea for euthanasia, absolutely not.
"But it is a plea for the same level of care and openness in all patients who are terminally ill.
"Our message is that euthanasia will not cause more grief. It was sometimes suggested that we didn't know what we were doing, and that euthanasia might be bad for the relatives."
Dr Swarte said there were lessons for medical personnel dealing with all terminally ill patients.
"It's very important to realise that the possibility of saying goodbye and everything they want to say is very important for the relatives, and the patients."
A spokeswoman for Cruse Bereavement Care told BBC News Online the organisation did not have a position for or against euthanasia, but aimed to support anyone who has been bereaved, no matter what the relationship was with the person who had died or the circumstances of the death.
She said: "The complexities of bereavement are such that if the bereaved person has had the opportunity to say goodbye and say some of the things they really want to say and to listen to the dying person's thoughts and feelings it can often make the experience more bearable.
"Sadly in many situations, such as sudden death, this is not possible."
The research is published in the British Medical Journal in a special issue focussing on death and bereavement.
It featured other studies including research suggesting doctors often over-estimate how long terminally-ill patients will live for, that they can be strongly affected by patients' deaths and that more debate is needed before legalising euthanasia can be considered.
The Cruse Bereavement Care helpline can be contacted on 0870 167 1677.