More than 1000 people remain in Australian-run offshore processing centres on Manus Island and Nauru, the vast majority of whom are genuine refugees.
Home Affairs officials have told a Senate committee there are 431 people left on Nauru, including 330 refugees and three children relocating to the United States later this month.
Another 26 people on Nauru are non-refugees, while 75 people are yet to have their claims for protection determined.
There are 584 men on Manus Island; 456 are refugees, 121 are non-refugees, and seven more have been offered protection because they face serious risks in their country of origin.
The committee heard 1246 people have come to Australia for medical treatment over the past five years.
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Home Affairs deputy commissioner Cheryl-anne Moy said 282 of these people later returned to Manus Island and Nauru.
"Those returns were generally prior to 2015," Ms Moy said.
In recent years, most people brought to Australia for medical treatment have launched court action to prevent their removal.
"Doctors have got them here, lawyers are preventing them from leaving," Home Affairs secretary Michael Pezzullo said.
Doctors have now been given a greater say in medical evacuations for asylum seekers, under laws which passed parliament last week, against the will of the government.
The immigration minister's discretion to block transfers on security grounds has been curtailed through the changes.
The laws have sparked a political brawl between the major parties, with the coalition accusing Labor of weakening border security by supporting the legislation.
