Two drunken 13-year-old girls had to be airlifted to hospital from the side of a mountain during the early hours.
Paramedics found one of the teenagers unconscious on Conwy Mountain on Tuesday, and mountain rescuers called in the RAF rescue helicopter.
Eleven others made their own way down the steep mountain towards Conwy and Dwygyfylchi.
North Wales Police said an investigation was under way to find how the teenagers got hold of the alcohol.
The two girls were taken to Ysbyty Gwynedd hospital at Bangor, Gwynedd.
A spokesman for the Ogwen Valley Mountain Rescue Team said it was 'unusual' call-out.
"Somebody had seen them on Conwy Mountain and called the ambulance," said Chris Lloyd.
"The local mountain rescue members were then called out at about half past midnight and because it was a long carry-out 22 squadron were requested," he added.
Mr Lloyd said other members of the group ran off, and there was concern that more casualties might be "scattered" on the mountainside.
Because of this the helicopter then flew back to check, he said.
"The police also met the others (as they got off the mountain) to make sure everyone was accounted for."
The incident finished at 0330 BST on Tuesday.
Mr Lloyd added it was unusual to "assist with intoxicated teenagers", but it is not the first time it had happened.
"We had a call-out about 10 years ago to a bothy above Dolgarrog, where someone was unconscious due to illness, but it turned out they were drunk," he said.
"It's not a mountain rescue issue, but we get called if it happens in rural areas," he added.
North Wales Police are appealing for information about the incident.
Inspector Ian Verburg, based at Llandudno, said that they were following up the matter with the girls and their parents, and were keen to discover where they obtained the alcohol.
He said anyone with information should contact Ps Tom Prytherch on 101 or Crime stoppers on 0800555111; 0845 6071001 (Welsh) 0845 6071002 (English) alternatively text 66767.