The walkers had got lost in the low cloud and rain on Cader Idris, joining forces to try to get off the mountain together.
Aberdyfi Search & Rescue Team were made aware of the walkers lost on Cader Idris at 5.30pm. One of the groups had been attempting the Three Peaks of Wales challenge for charity.
Team spokesman, Graham O’Hanlon, said: “They ended up coming down on the north rather than the south side of the mountain.
"Finding themselves on the edge of darkness, wet cold and tired, and having run off the edge of their map, they called for help.
“They had descended the stream gully from Mynydd Moel directly to Llyn Arran, which would have been difficult, unstable and steep.
"I suspect they might not have attempted that route if they could have seen what they were getting into.
"With an unstable scree slope, and everyone feeling cold and tired, it could easily have become a much more serious incident.”
Search and rescue volunteers moved up the hill to meet the group, provide extra lighting, and escort them down to the road by 8pm.
Mr O’Hanlon said: “People can enjoy the mountains in all manner of conditions, but in poor weather and low cloud it is very easy to become disorientated, and it makes those key map and compass skills all the more important in order to stay safe and get the most from the day.”