The group of more than 50 from the Cleveland Army Cadet Force in Middlesbrough were on a training exercise in the Mourne range in Co Down when they got into difficulties on Wednesday.
Children as young as 12 were among those rescued. Five suffered ankle injuries after slipping on wet stones and a number were treated for the effects of exposure, the MoD said.
ll Army cadets evacuated from the mountain following bad weather are safe, a spokesman said.
An Army spokesman added: "We can confirm that all Army cadets caught in today's inclement weather on the Mourne Mountains are safe and accounted for."
The Mournes are a range south of Belfast which is extremely popular with walkers but like all mountains the conditions can be unpredictable.
The group included children aged from 12-17.
Emergency services were called to the scenic Annalong Valley at around midday.
A Mourne Mountain Rescue spokesman said it was not a major incident but weather had caught them out.
He added: "It is nothing out of the ordinary.
"Everything is under control and within normal team procedure."
Northern Ireland Ambulance Service paramedics provided medical support.
Newcastle, Bangor and Kilkeel Coastguard Rescue Teams, and the UK Coastguard search and rescue helicopters based at Caernarfon and Prestwick, were on scene.
Also attending were the Irish Coastguard Rescue 116 helicopter, Mourne Mountain Rescue Team, Police Service of Northern Ireland (PSNI) and ambulance service.
An MoD spokesman said: "We are exceptionally grateful for their assistance."