A four-and-a-half hour operation involving 20 volunteers was staged to rescue three medical students from Snowdon in strong winds and heavy rain.
The students were on the Pyg track when they called for help
One of the trio, from London, was suffering from hypothermia and had to be carried down by stretcher before being taken to hospital in Bangor.
The three had raised the alarm while about 2,500ft (760m) up the mountain on the Pyg Track.
Rescuers have appealed to anyone using the mountain to watch the forecasts.
The four-and-a-half hour rescue operation had involved the Llanberis Mountain Rescue Team.
There was thick cloud throughout and the three walkers were suffering from the cold.
A spokesman for the rescue team said the trio had been wearing waterproof jackets but were otherwise not well equipped.
He advised anyone using the mountain to be aware that even if there was no snow, it was very cold and suitable clothing was vital.