The facility in Papua New Guinea is used by Australia to house asylum seekers
Papua New Guinea's Supreme Court has ruled that the detention of asylum seekers and refugees on Manus Island is unconstitutional.
Manus Island is used by Australia as a detention centre for asylum seekers who try to reach its shores by boat.
Five judges on the Supreme Court's bench ruled that the camp breached section 42 of the constitution and did not meet a requirement to respect "the rights and dignity of mankind".
Both the Australian and Papua New Guinea governments have been ordered to take "all steps necessary to cease and prevent the continued unconstitutional and illegal detention of the asylum seekers or transferees at the relocation centre".
Around 850 men are held on the island - around half of whom have been judged genuine refugees.